Upgrading a 300 carb Straight Six. (Pics) [Archive] - FSB Forums

: Upgrading a 300 carb Straight Six. (Pics)


AbandonedBronco
03-23-2009, 02:59 PM
Hey everyone, this is my first writeup on here. Seems that most everyone has the 302, 351, or a EFI 300, so I thought I'd give some eye candy to the carb 300 enthusiasts.

The stock carb 300 has about 120hp and 255tq. The engine is known to be a tank, and you definitely can't stop it. Unfortunately, you can't exactly get it going very quickly either.

Last summer I swapped out my stock log exhaust manifold for the dual manifolds from a stock fuel injected 4.9. (I'll have to dig up my pictures and put them in here too). The 1bbl exhaust had a 2" outlet, which is about a 3.1 square inch exit. The EFI manifolds have two 1.75" outlets. Together, that's about 4.8 square inches. About a 30% gain. I also went from the stock 1 7/8" exhaust to a high flow 2.5" exhaust. Not to mention the cat was original and was so plugged I was blowing manifold gaskets. The difference was amazing. Est. 145hp/270tq. Total cost from engine block to tailpipe: ~$400

This spring it was time for an intake upgrade. The stock Carter one barrel on the 300 is about 180 - 200cfm (heard quite a few different numbers). It does well up until around 3000 RPMs and then gives out. With the stock setup, you can't get it up much over 3000 anyway so this is okay. However, with a much higher flowing exhaust, it was time for some more carb.

After doing about a year of research (might as well since I had the time, not the money), the Offenhauser dual port intake with a Holley 390 was agreed to be a very good upgrade. I found one used from a guy who threw a rod in his engine for much less than new. Normal price was about $800, picked his up for about $300.

The hardest part was making an accelerator bracket for the engine since the stock bracket bolted to the stock intake. Just took some ingenuity.

After wading through and removing the stock tangle and mess of vacuum lines and removing the stock intake, I bolted the new intake in and connected the carb. It fired up nicely and after a little tuning we took it for a test drive. Even with a 3.00 rear end, it snapped the RPMs right up to around 4000 and definitely wanted more. Without some head building, I probably shouldn't be taking it much higher than that, although it seemed like it certainly wouldn't care. My easy going 300 has suddenly become a force to be reckoned with. I couldn't believe the difference, it basically felt like I just removing 1500lbs from the vehicle and it felt as light as a toy.
Est: 170hp / 290tq.

The new intake, prepped and ready to go.
https://www.supermotors.net/getfile/716717/fullsize/offenhauser-intake.jpg

Fitting on the Holley carb to check for accelerator bracket alignment.
https://www.supermotors.net/getfile/716719/fullsize/the-holley-390.jpg

Comparing the old Carter 1bbl with the new Holley 390.
https://www.supermotors.net/getfile/716721/fullsize/size-comparison.jpg

Here's a comparison of the venturi sizes. No wonder...
https://www.supermotors.net/getfile/716722/fullsize/venturi-comparison.jpg

My brother working away with the grinder making the cable bracket.
https://www.supermotors.net/getfile/716723/fullsize/grinding-the-bracket.jpg

The mostly stock engine bay, just ready and waiting.
https://www.supermotors.net/getfile/716725/fullsize/engine-bay.jpg

Another view of the engine bay.
https://www.supermotors.net/getfile/716727/fullsize/the-engine.jpg

Here's a view of the previous intake and exhaust. Gotta love the mess of vacuum lines.
https://www.supermotors.net/getfile/716728/fullsize/intake-and-exhaust.jpg

A view of the stock carb on the engine. It's put in some good work, but it's time to go.
https://www.supermotors.net/getfile/716729/fullsize/the-stock-carb.jpg

A cleaner view of the intake/exhaust with all the lines out of the way.
https://www.supermotors.net/getfile/716730/fullsize/a-cleaner-view.jpg

A clear view of the dual exhaust manifolds from the fuel injected 4.9. Those things are sweeeeet.
https://www.supermotors.net/getfile/716731/fullsize/intake-removed.jpg

The new intake set in place on the engine. No work required, it fits perfectly.
https://www.supermotors.net/getfile/716732/fullsize/new-intake.jpg

Here's me working away, torquing down the manifold bolts.
https://www.supermotors.net/getfile/716738/fullsize/workin.jpg

My Bronco with my brother's Jeep. Another awesome straight six. (4.0L high output.)
https://www.supermotors.net/getfile/716740/fullsize/bigger-is-better.jpg

The finished custom accelerator bracket. Simple, effective, and hidden from sight under the air cleaner.
https://www.supermotors.net/getfile/716741/fullsize/accelerator-bracket.jpg

Hooking up the necessary vacuum lines and hoses. There were so few, it took me a moment to believe it.
https://www.supermotors.net/getfile/716742/fullsize/hooking-the-lines-up.jpg

The final touch. Tuned, and ready to go.
https://www.supermotors.net/getfile/716743/fullsize/the-final-touch.jpg

Next on the list is a distributor recurve. This moves the distributor's vacuum advance from an emissions oriented curve to a performance curve and will really wake this whole setup right up. The kit cost $4 and is sitting on my work bench. After that, it's a head P&P (maybe this summer), and a cam. From what I've read, this should be setting the engine right around 210hp/325tq. Should have come like this from the factory...

justin
03-23-2009, 03:04 PM
Nicely done. I was planning to do an offy intake/Holly carb on my 77 but I've decided to just do a FI swap one day. Now put a 3G on it and a saginaw out of a E series w/ a 300!

Want to sell that Carter YF?

Optika1 illushun
03-23-2009, 03:12 PM
This is a great write up. i agree, 3G and saginaw pump would set it over the top, search though the threads and u should find a bolt on saginaw pump thread.

questions i didnt see answered for others. which y pipe did u use, and muffler. have u rejetted the carb or played with anything else?

also, dont forget for now u can swap to high lift rocker arms instead of the cam swap.

AbandonedBronco
03-23-2009, 03:14 PM
Nicely done. I was planning to do an offy intake/Holly carb on my 77 but I've decided to just do a FI swap one day. Now put a 3G on it and a saginaw out of a E series w/ a 300!

Want to sell that Carter YF?



Thanks. Driving to work this morning was a whole new experience. I loved it.
I thought about doing the FI swap, but I didn't like how finicky the stock computer was, and this was much more in my budget. Besides, this is much more unique. :)
A 3G is definitely on the list but first is a Saginaw! After all this work, I'm looking forward to one day being able to hear my engine over the sound of the power steering pump whining.



As for the carb, I have some parts carbs if you need some things, but I need to hang on to this one. We do have emissions here and I might need to swap it back in. There's no visual, so I'm clear there. But I figure if I can get an emissions oriented 1bbl to pass emissions with flying colors with NO emissions equipment whatsoever, I should be able to tune a 4bbl to pass our lax emissions laws. If not, I'll probably need to swap it back in to get it to pass.

This is a great write up. i agree, 3G and saginaw pump would set it over the top, search though the threads and u should find a bolt on saginaw pump thread.

questions i didnt see answered for others. which y pipe did u use, and muffler. have u rejetted the carb or played with anything else?

also, dont forget for now u can swap to high lift rocker arms instead of the cam swap.

I used a walker converter pipe made for the 4.9 EFI manifolds and it bolted right on perfectly and was dirt cheap. WLK-45166 The muffler was a turbo dynomax muffler and it sounds awesome. Here's a video of the exhaust with the 1bbl on there (haven't updated yet): http://www.youtube.com/watch?v=sHTK3Twq2Vo

JUST got it running last night. Haven't messed with jets or anything yet. That'll come next. Already drives great, so it's pretty close fortunately.

And I've heard mention of the higher lift Chevy rocker arm swap but I think I need different rocker studs on my head.

XDAILY
03-23-2009, 03:15 PM
Nice writeup and neat engine. Ive had an inline 6 in an 86 bronco before.

Mine was stock but I hear of some peps working these engines for impressive
numbers. Ive also seen a carbed Jeep with a worked inline that made some
impressive power and the exhaust sounded good too.

AbandonedBronco
03-23-2009, 03:19 PM
Yeah, there's a guy over on fordsix.com that had his professionally built and rebuilt. It's pushing out around 300hp/400tq.

Handy_andy_cv64
03-23-2009, 03:27 PM
I work at an emissions shop, and if you want the best chance of passing, install a zero-backpressure cat, if you haven't already. Use one with a Cali CARB EO number cat, as those are generally used by racers in Cali (there are eight-second EFI Mustangs and Camaros out in Cali) so that they still pass emissions. The 390-cfm has a very good chance at failing without a cat to back it up; and a zero-BP cat should not affect your numbers.

AbandonedBronco
03-23-2009, 03:31 PM
I work at an emissions shop, and if you want the best chance of passing, install a zero-backpressure cat, if you haven't already. Use one with a Cali CARB EO number cat, as those are generally used by racers in Cali (there are eight-second EFI Mustangs and Camaros out in Cali) so that they still pass emissions. The 390-cfm has a very good chance at failing without a cat to back it up; and a zero-BP cat should not affect your numbers.

Thanks for the info. Right now it has a high flow cat on it. (This one to be exact: Cat (http://store.summitracing.com/partdetail.asp?autofilter=1&part=WLK-15038&N=700+-99663+115&autoview=sku) ) I guess by no emissions equipment, I meant in the engine bay, like a smog pump and EGR valve and other components that effect how the carb itself operates. The cat is brand new as of last fall.

crash-harris
03-24-2009, 01:49 AM
By the time your pushing 300tq you'll want to start using forged parts. I think you may be fine though, but I'd ask FTF.

Btw, where did you get the recurve kit? And did they have one for the EFI dizzy?

Optika1 illushun
03-24-2009, 01:51 AM
why? the engine will only see 5,000 rpm at the most and forged isnt really needed.

rhauf
03-24-2009, 02:26 AM
why? the engine will only see 5,000 rpm at the most and forged isnt really needed.

:stupid

AbandonedBronco
03-24-2009, 10:13 AM
True, right now its probably at it's peak hp at 4000 - 4500 RPM and peak torque around 1500 - 2000. I doubt I'll rarely take it to 4500 unless I'm just in the mood. Plenty of go down low. 5000 would probably scare me.

I got the recurve kit at summitracing.com. Either way, it's a Mr. Gasket 925D. As for working on an EFI, I really don't know for sure. Mine already says "for a Ford '55 - '70 distributor", but it's the one everyone says to go with.

crash-harris
03-24-2009, 12:39 PM
I'll have to dig through the threads on the FSP forums and findout if I should use the same. And if 5k is going to scare you then you'll be fine with the stock cast pistons. Just remember that they like sheding their skirts, unlike most girls I went to high school with...

AbandonedBronco
03-25-2009, 01:44 PM
The thing you may need to look out for with the EFI is throwing off the computer, those things are sadly finicky. That would be what I'd worry about.

landtortise89
03-25-2009, 01:51 PM
btw justin nice write up. if anyone finds info on the recurve kit for the efi post it up. i am deffinatley interested in one. another cheap mod for the six is doing a 302 throttle body swap. I have been working on this for a while unfortunatley i have the expensive tps the one without the whip which is bigger and won't work on just any 302 throttle body. if you have the tps with a whip on it. it's a direct bolt on. I recommend doing a little boring on the upper intake.

crash-harris
03-25-2009, 02:01 PM
My build will consist of the 302/351 TB and a mild port n' polish job on the intake, but I'm doing that build to a complete drop-in for my wornout stock 300.

I want to go Megasquirt sometime down the road, after reading through the Megasquirt section on the FSP forums I still don't understand it completly though. I just hope my build won't send my stock PCM on the fritz!

AbandonedBronco
03-26-2009, 12:15 PM
If anyone is curious, I added all of the pictures from the exhaust upgrade I did last fall.


http://www.supermotors.net/registry/media/717393


Some highlight pictures for people just browsing the forums:

The pre-made pipes. These were a great buy. The tailpipe was 2.5" mandrel bend made just for the Bronco, and the Y collector was a 2.5" performance upgrade pipe made just for the 300 EFI manifolds. Saved me TONS of money and time. About $150 for the pair.
http://www.supermotors.net/getfile/717393/fullsize/082908141700.jpg

The dual EFI 300 manifolds, courtesy of LandTortise (and his help removing them). Says one thing about EFI vs. carb. 5 hours to take them off the EFI, 30 minutes to put them on the carb (including removing the original).
http://www.supermotors.net/getfile/717395/fullsize/081708125800.jpg

The stock and super restrictive 300 exhaust and EGR pipe.
http://www.supermotors.net/getfile/717396/fullsize/090308183200.jpg

A clear view of the 300 intake/exhaust ports with the manifolds removed. So easy working on an engine with everything on one side and out in the open.
http://www.supermotors.net/getfile/717397/fullsize/082408133500.jpg

New vs old. I couldn't believe how HUGE the stock cat was.
http://www.supermotors.net/getfile/717398/fullsize/090408180800.jpg

New pipe size vs. the stock pipe. 2 1/2" vs 1 7/8". It may not look like much, but one 2 1/2" exhaust pipe is almost as big as two 1 7/8" pipes. Quite a difference.
http://www.supermotors.net/getfile/717400/fullsize/090408180900.jpg

The original muffler. That's chunks of guts that blew out of the cat. So once exhaust got past the completely and horribly plugged cat, it had to work it's way around MORE cat that was in the muffler. No wonder I was blowing manifold gaskets.
http://www.supermotors.net/getfile/717399/fullsize/090408173600.jpg

New exhaust all installed and tightened. It sat SO nice and solid. I could lift myself off the ground with it.
http://www.supermotors.net/getfile/717403/fullsize/090608103500.jpg

I've seen some premade tailpipes that hang pretty low. This one was nice and snug under the body. I was very pleased.
http://www.supermotors.net/getfile/717404/fullsize/090608103700.jpg


The pictures were taken with my phone instead of my digital camera so the quality isn't as clear. Also, the link has more pictures and more writeups of the project.
Let me know what you think.

crash-harris
03-27-2009, 01:08 AM
Was that snake skin or braided metal?!

AbandonedBronco
03-27-2009, 07:30 AM
Was that snake skin or braided metal?!

lol

That was a sleeve of factory heat insulation.

Allison#55
03-30-2009, 03:59 PM
Where did you order the walker pipe from?

AbandonedBronco
03-30-2009, 04:11 PM
I got it from summitracing. You might be able to just order it from your local parts store too.
WLK-45166 was the part number for the Y-Pipe

Ronbo
04-09-2009, 07:40 AM
I noticed the manifold heater conversion on the 1 bbl. but it was missing on the 4 bbl. Will you be doing a write up on that also? This is great! I did this six years ago and the only parts different I see are: I used headers instead of the manifolds and MAYBE the cat, I went with a high flow unit from Summit. The muffler, tailpipe and the rest are identical! Did you have to plug the ports on your head for the A.I.R. injectors? And yes, you will need different rocker studs for a rocker swap. I still have the rocker arms in my tool box because of them. Again, super write up!

Ron

Ronbo
04-09-2009, 07:45 AM
I just saw your link to the cat, exact same one! Too funny. I have the 3G swap and the PMRG starter swap done also. Haven't gotten around to the saginaw conversion. You might not need the starter, headers were causing heat soak and when the starter went the whole she-bang had to come off. Thusly the smaller starter. If you haven't swapped out the low back seats yet, a set of highbacks from a 90's explorer will fit. It also allows you to recline.


Ron

AbandonedBronco
04-09-2009, 09:23 AM
I noticed the manifold heater conversion on the 1 bbl. but it was missing on the 4 bbl. Will you be doing a write up on that also? This is great! I did this six years ago and the only parts different I see are: I used headers instead of the manifolds and MAYBE the cat, I went with a high flow unit from Summit. The muffler, tailpipe and the rest are identical! Did you have to plug the ports on your head for the A.I.R. injectors? And yes, you will need different rocker studs for a rocker swap. I still have the rocker arms in my tool box because of them. Again, super write up!

I just saw your link to the cat, exact same one! Too funny. I have the 3G swap and the PMRG starter swap done also. Haven't gotten around to the saginaw conversion. You might not need the starter, headers were causing heat soak and when the starter went the whole she-bang had to come off. Thusly the smaller starter. If you haven't swapped out the low back seats yet, a set of highbacks from a 90's explorer will fit. It also allows you to recline.


Ron


Thanks for the props! I've been driving it a few weeks now and love it. Still having some tuning to do, like some off-idle stumble and stuff, but I know what to do to fix it (just need a little extra $$ since it's the most expensive jet on the carb), but it's been great, and the power difference is amazing. I'm also getting the same gas mileage as my 1bbl so I can't complain.

As for the manifold heat, the Offenhauser intake does come with the provision to bolt a stock exhaust manifold to it (unlike the Clifford intake), which would enable me to bolt the intake heat to it. However, the guy I bought the intake from had headers, and for some reason thought he had to "modify" the intake for them, so he welded the intake/exhaust connection shut. It would have taken a lot of extra work to cut the welded plate off, plane it smooth, etc, so that I could bolt my carb heat to it. So, I got a 4bbl carb heated spacer from a friend. It sits right under the carb and has coolant running through it.

This picture shows it:
http://www.supermotors.net/getfile/716742/fullsize/hooking-the-lines-up.jpg
You should be able to see the coolant line running from the heater core to right under the carb, and then out the other side.

I was lucky on mine because they didn't add the AIR injectors on the head until a year or two later, so I didn't have to worry about it. The only things I had to plug off were just some vacuum line ports and that was it.

That's awesome on the identical setup! :rockon :beer I'd like to see pics of yours if you have them. How do you like the headers? I thought about them, but didn't want the hassle I'd heard about, and for my application, EFI manifolds were way over my stock one anyway, and retain some of that original factory flavor. (Plus they were $50 instead of $200 - $400. No brainer.)


Low back seats to high back ones are high on the list. They were worn out when I got it and I bought some foam pads from a crafts store and put them under seat covers. It looks nice and is surprisingly comfortable, even on 10+ hour trips, so I haven't minded too much. But I'd love to be able to recline, and have a head rest. If nothing else, for the rear ended safety sake.

Have you ever port and polished your head? If not, that's supposed to REALLY wake it up. It brings the exhaust and the intake upgrades together. I like what I heard someone say, "the 300 head isn't biased. It's equally restrictive on both ends."

Ronbo
04-10-2009, 08:17 AM
If I remember right, I was in AZ when I bought the headers. The local boneyard (only one in 100+ miles) was REALLY proud of their parts and thats why I went with the headers, came out about the same price. I can't comment on how they work compared to the manifolds because I haven't ridden in a vehicle with them yet. I STILL remember (six years later) the difference in performance in doing that swap. Took two days to get everything sorted out and when I took that first trip down the road, holy crap! Night and day! I had done the exhaust about a year earlier and it made such a difference I knew there had to be more. I have not messed with the head other than trying the rocker arm swap so, no on the port and polishing. I figure we are getting about as much as can be had out of these beasts without laying down some serious dinero $$$$. Enjoy!!

tlg013
04-16-2009, 06:07 PM
Great setup on your I6! Those pictures are giving me an idea how good mine is gonna look. Nice....I plan on doing almost the same thing to my I6 as you except I'm going to take it a bit further. I'm getting a cam from comp(grind 252H). Also plan on picking up a head from a guy and am going to port and polish it and set up some roller rocker arms on it. I'm getting the same offen. dual plane intake, except I'm gonna use a 470CFM holley truck avenger carb so I can handle the hills good and I have some headers. I also plan to get one of the awesome dizzys from Fordsix(little expensive, but easy cause it only has one hot wire to hook up, and better performance). Gonna gap the plugs to .055" and hope to get some good advance on the timing. I'm hopeing I am gonna get 350+ torque at around 2000-2500 RPM. Only problems I'm still running into is the return line/vapor canister on the little 1bbl. and to block off the heat riser on the offen. intake. I hope I can do it all at the same time too. But you know how that always goes. When I do it ill add some pics and stuff.

AbandonedBronco
04-16-2009, 06:24 PM
Hey, sounds like you'll have a pretty sweet setup when you're done. The Comp 252 is on my Christmas list as well, as is the dizzy (I like it because they'll custom make it for your vehicle, and it includes the dist, coil, and ignition module, all in one.) The 470 truck avenger was another option I looked at, but Holley told me it was strictly made for power and off-roading, so it would never get the greatest mileage. So I went with the 390.
I wouldn't put it past your setup to have 350+ torque without even batting an eye, especially with the headers and a P&P.
However, on the Offy intake, don't even mess with the heat riser opening. For some reason, there's a rumor that you have to seal it up (the guy I got my used one from did it to mine), and it's a complete waste of time. It's just an empty opening and sealing it will cost you time and money for no reason what-so-ever. ;)

Have fun and post pics! If you do it all at once, which it sounds like you are, you're not going to know WHAT hit you when you first step on the gas. I love it, and I'm not even done.

tlg013
04-17-2009, 12:49 PM
Good point on the carb. Didn't think about the mileage issue. O well, I'll take the power I guess cause I don't really know if its gonna be a daily driver. Good point on the intake, thanks for the advice. So what did you do about your vapor canister and return line??

AbandonedBronco
04-17-2009, 12:53 PM
The vapor canister and return line was something I was really bummed about. I, personally, like a very clean running vehicle, and have even thought about retrofitting emissions equipment into my 4bbl to deal with this. As for the return line, there just wasn't a port out of the carb to deal with it, so I had to cap off the canister and leave it unused. Fortunately, though, the 390 has two ports that vent fumes up and back into the air cleaner to be sucked back through and be burned again. Maybe that just takes care of the whole deal.

I'd love to get a 470 later on down the road, but I use the Bronco for 95% daily driving and 5% camping and off-roading (wish it was more), so I had to get a carb that suited the higher percentage of needs. That being the case, I went with the one that gave me the best mileage. It'd be sweet to have a tuned 470 sitting on the shelf so when I go camping/off-roading, I can swap carbs.

Sojourner
05-13-2009, 02:53 PM
AbandonedBronco- What kind of gas mileage are you getting now? My '86 is has a I6 and I was thinking about slowly collecting all of the parts necessary for your upgrade. The only concern I have is what the final MPG will be.

AbandonedBronco
05-13-2009, 02:58 PM
I am still in the fine tuning process, since stock jets on the Holley 390 aren't exactly ideal for the 300, but so far, better than stock around town, lower than stock on the interstate. I also don't want to say what the numbers have been because I believe I found a torn fuel gasket in my carb, so gas just leaking out has probably been detrimental to my mileage. Just a guess though. :toothless
Got the rebuild kit in hand, but am in the process of moving, so I'll report back when it's tightened up.

Some have reported 15town/19highway with a well tuned 4bbl.

Sojourner
05-15-2009, 11:20 AM
Some have reported 15town/19highway with a well tuned 4bbl.

SOLD!!! :thumbup

Please keep us posted. I love my 300, just wish it was a little more rabbit and a little less turtle. :doh0715:

crash-harris
05-15-2009, 05:18 PM
There's tons of things you can do to the six, you just have to be willing and patient. Abandoned can vouch for this, there is a guy over at the Fordsix (www.fordsix.com) forums that runs the 300 in a dragstar and does well (he's in the process of building another with a 300 that now has a Duesenburg DOHC).

88_CdA_bronc
05-28-2009, 05:25 AM
Great write-up, AB!

It's about time someone with an I6 found some money so I can read about what they did to improve their Bronco! IMO, there's never enough info about the great 300. I too have a 300 in my '83 and I have started saving to perform these very same upgrades in several years. Keep it up, never stop experimenting and certainly never stop posting!

Great job!

AbandonedBronco
05-28-2009, 11:51 AM
Thanks! Yeah, it's been a lot of fun, and in the end (as far as big mods go), wasn't all that expensive. It was about $800 and about half the cost went into a full exhaust, which the Bronco needed anyway. It's crazy going from a restrictive 1bbl to feeling secondaries opening up and setting you back in your seat. =P

AbandonedBronco
06-29-2009, 03:52 PM
http://www.supermotors.net/getfile/740233/thumbnail/740233.jpg (http://www.supermotors.net/registry/media/740233)

Hit a couple of easy trails this weekend. It was nice, powerful, and effortless, I loved it.

Also did a bit of re-jetting on the carb and it runs so much better and seems to be getting better gas mileage. Did a full rebuild on the carb while it was all apart.
If anyone goes this route with their 300, the stock jets on the 390 are much too small (I believe they were designed as a replacement to a mid 200ci engine replacement).

Main jet: Stock 51. Upgraded to a 53
Power valve: Stock 6.5. Upgraded to an 8.5
Accelerator Pump Squirter: Stock 25. Upgraded to a 35, but recommend a 37. Don't think the 35 is big enough yet, but very close.

Was lean on all accounts before, and made it run pretty poorly, bogging, acceleration loss, etc. Went for a drive yesterday after all was said and done, and hit a hill at 55mph. Barely had to touch the gas to make it climb and it felt so effortless. I'm in love.

Of course, thinking back to when I FIRST got the Bronco, it ran so poorly I would have had to have done the same hill at 20mph with the hazards on. It's come a long way.



Added:

Another video (6 - 8 - 09)

http://www.supermotors.net/getfile/742534/thumbnail/742534.jpg (http://www.supermotors.net/registry/media/742534)

Rudster
07-16-2009, 07:04 PM
Great write-up.

While I can't perform the carb/intake swap (California), the exhaust is something I am strongly considering.

Thanks for sharing.
~Rudster~

AbandonedBronco
07-17-2009, 10:52 AM
Hey Rudster,
The exhaust might even be difficult because all of the emissions equipment ties in with the stock exhaust manifold.
I imagine being a CA vehicle, you have any oxygen sensor too.
It would take some fab work, but you could do it. Unless you do it with some cheap copper tubing, you could make it look like stock too. There's an oxygen sensor port on the downpipe that you can use. Then, there's an EGR pipe port on the EFI manifolds. You'd have to bend some tube to hook it up right. Considering that the stock was just bent tubing, it's not going to be much different.

The difficult one, though, is going to be the smog pump, since there won't be a port left for it. You could hook it up by drilling a hole into the front EFI manifold and welding a bung to it the same thread as the smog hookup. It'd just take some work.

Doable though!

As for the carb/intake. I believe Holley sells emissions compliant 4bbl carbs, might be worth looking into too.

justin
07-22-2009, 03:28 PM
What did you tune or what jet did you replace to get rid of your off-idle stumble.

I'm having the same issue right now with my YF......I've tuned all I can and can't get rid of it. The weirdest part is that I don't always have it, sometimes I can pull off from a stop light just fine and other times it will stumble all over itself until I back off and let it get rolling first.

Rudster
07-22-2009, 05:42 PM
Hey Rudster,
The exhaust might even be difficult because all of the emissions equipment ties in with the stock exhaust manifold.
I imagine being a CA vehicle, you have any oxygen sensor too.
It would take some fab work, but you could do it. Unless you do it with some cheap copper tubing, you could make it look like stock too. There's an oxygen sensor port on the downpipe that you can use. Then, there's an EGR pipe port on the EFI manifolds. You'd have to bend some tube to hook it up right. Considering that the stock was just bent tubing, it's not going to be much different.

The difficult one, though, is going to be the smog pump, since there won't be a port left for it. You could hook it up by drilling a hole into the front EFI manifold and welding a bung to it the same thread as the smog hookup. It'd just take some work.

Doable though!

As for the carb/intake. I believe Holley sells emissions compliant 4bbl carbs, might be worth looking into too.

Right. Will need to investigate. Thank you sir.

AbandonedBronco
07-23-2009, 04:15 PM
What did you tune or what jet did you replace to get rid of your off-idle stumble.

I'm having the same issue right now with my YF......I've tuned all I can and can't get rid of it. The weirdest part is that I don't always have it, sometimes I can pull off from a stop light just fine and other times it will stumble all over itself until I back off and let it get rolling first.

I was actually having the same issue with the YF before I switched over. Even if you've rebuilt it, did you check to see if your main jet and metering rod were worn? There's actually physical contact when the metering rod goes down into the jet, so it'll wear the jet into an oval, and wear the sides of the metering rod so it doesn't sit right. That could be a possibility.
The other is to maybe try a larger jet size. It might be starving for fuel on takeoff. I know with the 4bbl, that's what the issue was. It was falling flat on it's face and just a 0.002" increase in jet size made it take off 95% better. Crazy how the little differences do a lot.

justin
07-23-2009, 04:57 PM
I was actually having the same issue with the YF before I switched over. Even if you've rebuilt it, did you check to see if your main jet and metering rod were worn? There's actually physical contact when the metering rod goes down into the jet, so it'll wear the jet into an oval, and wear the sides of the metering rod so it doesn't sit right. That could be a possibility.
The other is to maybe try a larger jet size. It might be starving for fuel on takeoff. I know with the 4bbl, that's what the issue was. It was falling flat on it's face and just a 0.002" increase in jet size made it take off 95% better. Crazy how the little differences do a lot.

I've rebuilt it a few times but I don't remember if the metering rod was worn or not. I'll have to crack it open and take a look.

I'll look into a jet upgrade as well, regardless, it could use a little more fuel as its a bit on the lean side. Its really annoying, especially when I'm stopped going up a hill.

justin
07-23-2009, 04:58 PM
I was actually having the same issue with the YF before I switched over. Even if you've rebuilt it, did you check to see if your main jet and metering rod were worn? There's actually physical contact when the metering rod goes down into the jet, so it'll wear the jet into an oval, and wear the sides of the metering rod so it doesn't sit right. That could be a possibility.
The other is to maybe try a larger jet size. It might be starving for fuel on takeoff. I know with the 4bbl, that's what the issue was. It was falling flat on it's face and just a 0.002" increase in jet size made it take off 95% better. Crazy how the little differences do a lot.

I've rebuilt it a few times but I don't remember if the metering rod had worn into the jet or not. I'll have to crack it open and take a look.

I'll look into a jet upgrade as well, regardless, it could use a little more fuel as its a bit on the lean side. Its really annoying, especially when I'm stopped going up a hill.

duff
07-29-2009, 09:45 PM
Miss my 85 I6 Bronco. At 90K I did the head, replaced the Carb with one from an E350
(recommended by a rebuilder) and replaced the TFI with a Duraspak. It ran better than new
and got 18MGP.

duff
07-29-2009, 09:45 PM
Miss my 85 I6 Bronco. At 90K I did the head, replaced the Carb with one from an E350
(recommended by a rebuilder) and replaced the TFI with a Duraspark. It ran better than new
and got 18MGP.

1965 pony
08-04-2009, 12:25 PM
I was wondering what gears you have in the bronco, and what trans, then what mpg do you see from it on a daily basis?

I have a 1978 F150 SWB 4x4 with a C6 and NP205 with 3.54:1 gears, and I am thinking of swapping in the 300 from a 1982 F100, and put the newer manifolds on the exhaust.

Thanks in advance.

85f150
08-09-2009, 02:10 PM
5000 would probably scare me.


It's not that bad, I've only thrown new rod & main bearings in mine because of doing it a couple times. It seems to really beat on them and make the engine a little louder. But depending on the gear selection you don't always have the choice, when you need to get out of a situation.

Heated carb's on the inliners are a must for anywhere that see's 40F's and lower. I still have the single barrel, because I have come across an intake that I like the design of yet, not to mention trying to get things lined up for a 4BT instead.

I found a good adpater off chebbies for heating, and it was definately good to get rid of the electronic "carb":

http://www.supermotors.net/getfile/265598/fullsize/front-shot-carb-adpt.jpg

Rock Fox
08-16-2009, 06:10 PM
This is probably a stupid question but, how did you decide which way to mount up the Holley? I've got a very similar setup: Offy dual port intake, 390 Holley, dual long tube headers, dual into single exhaust, RV cam. Got the intake and carb used seperately so was unsure as to which way to bolt up. Tried them both and after much discussion decided on primaries to long runners and secondaries to short runners. The reasoning was long runners promote better atomization and the short runners would be better for dumping the fuel when secondaries were opened. This also solved the throttle cable problem, I used one from an F.I 5.0 to keep the pull action. I still have some tuning to do but it runs real strong, doesnt stumble and will break the street 31's loose when I stand on it in third. Any insight would help.

AbandonedBronco
08-25-2009, 12:52 PM
Hey Rock Fox, sounds like it's running really nice. Do you have it set up with the throttle cable linkage towards the firewall and the fuel bowls on the passenger and drivers' side? If so, that's how I have mine set up. It was recommended to be oriented that way by Offenhauser since that's the way they designed it. If it was just the regular Offenhauser intake, it wouldn't matter which way the carb was oriented, but the DP is pretty specific.


1965 pony:
Right now, I have 30" tires with a 3.00 rear and a 4spd SROD with overdrive. It seems to do really well, but I'm still not quite up to the gas mileage of the 1bbl. Of course, with the 1bbl I used to go 65 on the interstate (and get 20mpg) and with the 4bbl I have a tendency to do 80+ mph so your miles may vary. :duh
However, when I'd push the 1bbl to 75 or so, I usually averaged 17 and with the 4bbl I'm getting about 16, so it's getting close. I think with a touch more tuning, the port and polish and I have in mind, and a hotter ignition system, it'll reach the 18 - 20mpg some get with their 4bbls (at 70 - 80mph no less).

Rock Fox
08-25-2009, 11:39 PM
Could you post some pics from the firewall side? I have my carb mounted just opposite from yours, I couldn't find any info on which way to go (looks like I'll be changing that again). Did you re-use the factory cable? Any help is appreciated.

AbandonedBronco
08-26-2009, 10:43 AM
I'll try to get some pics.

I reused the factory cable for a little while, but since the 1bbl sat higher than the 4bbl, it had to angle down pretty hard to reach the linkage. It was binding all the time and made for difficult driving. Eventually, I just went to the parts store and bought a $15 generic cable and it works great. The bracket you see in the pictures was one I made myself for about $5 and I bolted it to the two holes in the intake that were originally used to bolt to the stock exhaust manifold. It's worked great.

The reason for the carb orientation is because the two planes in the DP manifold were set up for the primaries and secondaries. The primaries go towards the engine, and the secondaries away. This is because the two planes in the manifold are different. One's about an inch tall and the other is about 1/2 an inch tall. The half inch tall plane has a higher velocity, which helps when the secondaries kick in. If you have the primaries going into the smaller plane, you'll restrict the fuel flow at lower speeds since the velocity won't be there. I think I'm remembering all of that correctly.:toothless

86turbodsl
08-27-2009, 09:17 PM
You're basically heading down the road I went down on my last truck. 81 F150 w/ 300 six. Engine was shot, so I picked up a 300 from a 79 F350 or something like that. It had a forged crank and forged rods. Supposedly a one year only thing. Went 30 over, rebuild everything. Steel timing gears, good rings, comp cams 260H, the whole deal. It came with that same offy intake, and a set of headers. 3-2 w/glasspacks. Picked up a holley 390 for it too. It was a baddass truck for sure. But the damn carb would ice up bad when it was cold out. (Michigan UP truck) I cut into the headers and ran pipes up to the little chamber right under the carb. The carb heater worked good, but had overheating issues with the carb in warm weather then. ended up ripping out the whole thing and putting 88 EFI intake on it, with clifford 3-2-1 headers for EFI. O2 sensor, the whole deal. It didn't like the stock computer and ran lean anyway, so I picked up 19lb mustang EFI injectors, made a custom adjustable fuel pressure regulator and tried about 3 different eec4-s. I worked at Ford powertrain at the time, and unfortunately the EEC4 stuff was on the way out and nobody had an R-CON or development ECMS sitting around anymore, so I couldn't tune the cam changes into a stock ecm. I ended up making an adapter harness for the EEC4 plug and put a DFI in it. Driveability was a lot better, but I never finished the cal. The truck rusted to oblivion and I gave the motor with about 5000 miles on it to a buddy and he gave me a 78 400M drivetrain in trade. I will say one thing though. With that DFI, 260h, headers and 19lb injectors, with a set of 33's, and 3.50 gears, it would ROAST the tires. That was the fastest 300 six F150 I ever rode in. The same torque they always had, and a top end that ran until about 4500-5000 instead of the normal 3500. Fun truck, but I moved on to turbo diesels and put the gas engines away. Enjoy the 300! It's a great bulletproof engine. About the lowest warranty cost engine Ford ever made.

taylor
08-30-2009, 08:23 PM
hey the 300 looks good so far. i have one in my 1977 f-100, and did the same thing. stock carb was shot, leaks all over intake and exhaust manifolds, so i replaced it all. holley 390 for starters, offenhouser intake manifold, hot shot headers to a straight pipe with dual cherry bombs. switched the distributer to electronic, new coil, actually all new ignition. new fuel pump, wires plugs, and then had the head shaved, a 3 way valve job, new springs and valves, basicly reworked. next thing im going for is a cam. my one suggestion to you is to get a bigger airfilter. i had that same one thinking 6cyl= small motor= small filter, but its a 300 ci motor, and wants to breath. also have you checked out clifford.com? great site for building l6's. but they are alittle pricey.

AbandonedBronco
08-31-2009, 12:11 PM
Yup, that's one of the reasons I did the conversion. I never could get the stock carb to run right, and I couldn't get the manifolds to stop leaking. Decided that, while I was replacing it all, I'd give it a bit of an upgrade. Definitely worth it.
I bet your truck ran a touch better after doing all that in one go! There's still a few things on that list that I'm wanting to do with mine, mainly the ignition and then a full head reworking (the biggest bottleneck).

I'll have to look into another air cleaner, but it's probably a ways down the road. I bought the intake used, and it came with the intake, carb, and the air filter for $300 so I wasn't going to complain!

Scatman
09-24-2009, 09:42 PM
I used to have a 300 in my 84 F150. I had the Offenhauser DP with a header and a Holley 390. No doubt it was a great and reliable motor, but it got tired. It started making some noise in the #5 cylinder and I decided it wasn't going to cost much more to do a swap with a motor I built myself. The 460 had way more power and no problems making 500ft-lbs like it was nothing. My mileage is actually better now with the 460. Anyway, for those of you looking for an inexpensive ignition upgrade for the 300 (or any of these Ford motors really), you should try the Chevy HEI swap using stock parts and recurve a Duraspark II distributor. There's a writeup for both here:

http://www.gofastforless.com/

I switched to an Accel aftermarket ignition during the 460 swap, but it didn't last long before the module blew up. Went back to the stock HEI and it's still working great. Hope this helps some of you budget builders.

AbandonedBronco
11-16-2009, 11:34 AM
Well, thought this was a fun update, so I thought I'd share.

Been working on tuning and tweaking the 4bbl for a few months, trying to iron out the kinks, learn how it operates, etc. I had been continually getting more and more nervous because I am required to pass emissions here, and even though I went headlong into a 4bbl upgrade and engine remodification, I had no idea if it'd ever even pass. I took my chances.

I recently hooked up an O2 sensor into the exhaust to see how it was doing, and it was running really rich. Tuned the jets way down to some 49s, and it seemed to do a lot better. Decided to run it over to an emissions station just to see how it'd do and maybe give myself some guidance on how it was running. I only had to the end of the month, so if it was going to fail I wanted to know by how much and get some clues as to what I could do to fix it.
Little did I expect, but it passed on my first try! I couldn't believe it. ((It actually failed the idle test but the guy at the shop (who used to be a performance carb tuner) looked at the numbers and told me it was just idling a tad rich. A 1/4 turn on the idle mixture screws fixed that and I was good to go.))

It actually passed better than the stock 1bbl did. I spent two months last year tweaking that stupid thing to get it to pass, and the Holley 390 passed this year without a hitch with no emissions equipment (except for a cat). Score.

Felix.
12-03-2009, 03:09 PM
https://www.supermotors.net/getfile/716732/fullsize/new-intake.jpg

I did the same set on my '85 F-150 years back... huge difference.
I used Clifford two piece headers instead of the stock EFI manifolds.
I also (because 15 years ago I had more money than brains) chromed the "Powered By Ford" valve cover and side pushrod cover :thumbup

84redbronco
03-02-2010, 02:24 AM
I have been following your progress on trying to get better gas mileage out of this setup as I have almost the same. I too have been getting 8-10 on this '84 since I bought it last year. I have a C6 3 speed with 33X12.5 tires. It's a daily driver seeing speeds around 35-40 mostly-could probably use an overdrive for highway use. After reading through your progress it has prompted me to examine more carefully the powervalve and dizzy timing curves, which I have just started to experiment with. I have one question though, for anyone that is, I have a Carter Competition 390 on an Offy intake and it is orientated on the intake with the electric choke to the passenger fender/choke butterfly towards the radiator, which I am assuming made for easy hook-up to the firewall linkage. Not sure if I have a dual plane or single plane manifold as I have not yet taken the carb off(just noticed that it may be stamped on the manifold), but if I have either one, will this carb orientation have negative effects with either manifold? It starts and runs fine, just trying to get above the 15mpg mark-better yet, 18-19. Good thing gas prices are not what they used to be or the Bronco might get parked. I will continue to follow your posts to see what you finally top out at.

AbandonedBronco
03-02-2010, 10:21 AM
I have been following your progress on trying to get better gas mileage out of this setup as I have almost the same. I too have been getting 8-10 on this '84 since I bought it last year. I have a C6 3 speed with 33X12.5 tires. It's a daily driver seeing speeds around 35-40 mostly-could probably use an overdrive for highway use. After reading through your progress it has prompted me to examine more carefully the powervalve and dizzy timing curves, which I have just started to experiment with. I have one question though, for anyone that is, I have a Carter Competition 390 on an Offy intake and it is orientated on the intake with the electric choke to the passenger fender/choke butterfly towards the radiator, which I am assuming made for easy hook-up to the firewall linkage. Not sure if I have a dual plane or single plane manifold as I have not yet taken the carb off(just noticed that it may be stamped on the manifold), but if I have either one, will this carb orientation have negative effects with either manifold? It starts and runs fine, just trying to get above the 15mpg mark-better yet, 18-19. Good thing gas prices are not what they used to be or the Bronco might get parked. I will continue to follow your posts to see what you finally top out at.

Hi 84redbronco.
8 - 10 is definitely low for the setup you have, even with 33s and a C6 (not that those help much.)
I've never heard of a Carter Competition 390 so I can't give any info there. But as for the intake, if you have the Dual-Port (which, yeah, you can quickly just see if it's cast into the intake), the carb can ONLY be put on one way, and one way only. Both primaries need to go towards the engine and both secondaries need to go towards the fender. If it's backwards, it gets all screwed up. (Of course, it'd be even worse if the primaries and secondaries are facing towards the front and rear of the vehicle.)
The other thing that'll screw up a dual-port is if someone put a spacer underneath the carb that doesn't have individual runners.
If it has a spacer, it has to be like this one:
http://www.pacificperformanceracing.com/images/products/chrome/phenolic-carb-spacer.jpg
Not:
http://www.pacificperformanceracing.com/images/products/carburetors/aluminum%20carb%20spacer.jpg


Other than that, yeah, the distributor timing, jetting, powervalve tuning etc. have helped quite a bit. My last trip I was able to pull around 15.6mpg @ 65, so it's been going up. It was also around 15 degrees out in the middle of winter, and it's also still running a little rich. It's impressive how gas mileage can just keep going up and up with tweaks.
Putting an oxygen sensor on it really helped too.
http://fullsizebronco.com/forum/showthread.php?t=161438


Good luck! :thumbup Keep us posted.

84redbronco
03-02-2010, 11:23 PM
Abandoned,
Thanks for the info., I'll see what intake I actually have.

84redbronco
03-03-2010, 04:46 AM
I had a chance to look at the intake and all that is stamped on it is Offenhauser. I won't know for sure unless I take the carb off. I just have started driving it again due to a starter problem. After reading through the threads on this post I decided to check plugs etc. All looked clean, not rich or lean, except the one by the firewall was a little wet, not oily. I checked these of course after a shutoff at idle which is not the best indicator while during driving conditions. Keeping in mind that I am not having any severe issues, just trying to get the most out of the engine a little at a time as you are doing, I just happen to have your info. to build on and hoping to offer something as well to ther readers on this site. I had previously reset the mixture screws and it seemed to alleviate some of the slight off start stumble. After the checking of the plugs, I advanced the distributor a little by eye and tightened all the belts as I noticed they could use it. I went to start it up and the sound was awful. Since I bought it a year ago, I always thought that the starter didn't sound right. On this occassion, it sounded much worse, almost like it was out of time/not enough advance/starter really acting up. I then backed iof the timing about half as much as I initially moved it and loosed up on the belts about half as much as I had tightened them and went to start it again, this time the starter hung up and stayed running with the ignition off and it quit before I could get the battery terminals off. I have since replaced the starter, which the local auto place checked and said was still good, and bought their best relay, which I had purchased before only a few months ago, but only the economy brand the first time. I bought another relay due to the information I obtained by reading through this site and since many readers have had multiple relay issues and the starter manufacturer recommened it as well. The sound of the new starter is SWEET and I am back in business. On the drive to work today I noticed there was a slight knocking when cruising at about 35 mph when there was a slight load on the engine, it went away when I applied a little more gas pedal to engage the secondaries/power valve-not sure which one it felt like or if I let off the gas a little it went away. Am I safe to say that I need to go a little bit more to the original position on the distributor? Not sure where my timing is degreed at as I can't seem to locate my light. Also, what powervalve have you wound up with and are you satisfied where it is at now? I have heard some that say to take your vacuum reading while cruising and divide by 2 and pick the next lowest powervalve and I have heard others say to use your vacuum reading while in gear at idle and pick the valve two numbers down from this reading-which one is it? Also, what fuel needles did you end up going with? I know our two carbs are different, but they might not be that much different-a starting point atleast. I need to get a fuel pressure regulator to make sure that I am running 5.5lbs. of fuel to the carb as I may be getting seapage from the needle seats wether from wear or gas pressure that may be contributing to my poor mileage. I might try the O2 sensor as well using the volt meter as I can do that my self and would be a cheap start. Atleast the sensor will already be there if I decide to go with a guage later. Should I go with a wide-band sensor for more accurate guage readings later on, but still be able to use the voltmeter on initial installation? Sorry if this is lengthy or if this might be considered thread jacking-I am new to the site and just trying to offer up some information that others might could use especially while helping my situation and given the fact that it seems so many readers seem to give up on the 4 barrel carb conversion or are satisfied with the poor mileage. I don't know if you will ever get back to 19mpg as you did with your previous setup, but you should get alot closer than where I am at now if you keep your foot out of it, but it doesn't hurt to exhaust all possibilities now does it?

AbandonedBronco
03-03-2010, 11:40 AM
If you don't have dual-port stamped on it, you most likely have the Offenhauser C.

http://www.summitracing.com/parts/OFY-6227C/?rtype=10

They make the DP and the C. DP is for more of a stock replacement with low end torque whereas the C is more for a higher performance engine, but gives up the low end in favor of higher revs. Both have their pluses and minuses. If you have the C, the carb can be sitting on there any old way you want it, so the orientation info from earlier is irrelevant. :)

The pinging under acceleration sounds like you might have a little too much advance. Sometimes though, you can advance it more and then reduce your vacuum advance canister on the distributor itself. There's also recurve kits that'll allow the advance to come in quicker, which can help with mileage. The whole timing curve on the stock distributor is set up for emissions. Oh, that reminds me, you DO have an '84, which originally came with an electronic computer controlled carb and distributor. Do you still have the computer controlled distributor in there? If so, you'll NEVER get it running right, or get very good mileage, until you swap it out. It's sitting there looking for signals from the computer for the timing advance, which is looking for signals from the 1bbl that used to be on there. If you still have the feedback distributor, the first priority would be to get rid of it and get a Duraspark II. You'll be in for a treat when you swap it out.

From what I've read everywhere, it's vacuum at idle divided by 2 for the powervalve. Mine sits at around 18 or so, so I went with an 8.5. I liked it, but eventually swapped it out for an expensive dual stage. ($35 vs $10). It opens half way at 5.5lbs and then all the way at 10.5lbs. of vacuum. It saves a lot on gas and only REALLY opens up when I floor it. But also doesn't leave me running lean when I need just a little bit of power. They're more for daily driver, distance driving, etc. since they can damage a race engine.

Currently, I have 52 size jets. I had 53s for a bit, but they were still a little rich on the O2, but ran really nice. Haven't had a chance to try these out yet since I stripped a fuel bowl bolt on installation. :doh0715: Currently have a backup carb on there. Runs terrible.


I should really check out my fuel pressure. I have no idea what it's at. Who knows, it may be another issue I'm facing. Never thought about that. Worth looking in to!


I'm still just hopeful on 18 - 20 since I know a few guys who achieve it with the same setup I do. It gives me a goal at least. Why be satisfied with sub par?

84redbronco
03-04-2010, 08:09 AM
The previous owner bought my '84 as a fixer-up and resell. The vehicle might have had one more owners before the original, but the story is that the vehicle was originally a V-8 4-speed manual and something happened to the engine and someone had the 300 already or decided to aquire one. The auto is a ratchet type shifter in place of where the manual gear shift hole in the tunnel. The vehicle supposedly came from out west and shows 98,000 on the odometer. Without sounding stupid or from just being lazy, how do I tell which distributor I have since I am not firmiliar with Ford applications or distributor specifics for that matter? I retarded the distributor when I got home and atleast checked the vacuum on the distributor and it is atleast holding vacuum. So I take it you now have a dual stage 5.5/10.5 powervalve? What brand plugs/# and gap are you running? I'm pulling for you as far as getting a best possible at around 18-20, I know I would be very satisfied at that point.

84redbronco
03-05-2010, 09:12 AM
I retarded the timing a little (clockwise on the distributor) and the predetonation ping is gone now. I remembered something to this effect that you had mentioned at one time I believe that this engine requires different turning direction of the distributor. Prior, I had mistakenly went a little counter clockwise thinking I was retarding the timing to get rid of the slight ping. It did not ping any worse, just may be a little more often and in a different RPM range/throttle position. Same as before, it stopped pinging with a little more throttle applied, but I do not no if it would ping any more in the upper RPM range as I rarely try and wind the engine out. I'm glad the ping went away as I was beginning to wonder because pre-detonation in this engine seems to sound like a rod knock to me. I will try this for a while and slowly initiate applying your information as time/funds permit.

AbandonedBronco
03-05-2010, 11:20 AM
Yup, the distributor spins the opposite direction on the I6 than the V8s. Good to keep in mind.

The distributor should be really easy to tell which one it is. If it's a Duraspark II, it'll have a vacuum line running from the carb or manifold to the vacuum advance canister on the distributor that'll look like this:

http://info.rockauto.com/getimage/getimage.php?imagekey=1130628&imageurl=http%3A//www.cardone.com/Imagesftp/84/842669-01.jpg

http://www.setyourtiming.com/images/Vaccumadvance.jpg


The feedback distributor won't have this since the advance is set by the computer.



Right now, I'm using just stock motorcraft plugs and stock gap. I'd eventually like to get one of these, which allows the widest gap and hottest spark possible. Just a little $$ at the moment.

http://www.performancedistributors.com/fordssdui.htm

They're sweet because the ignition module, coil, and distributor is all one unit.



Forgot about your question on the wideband sensor. I've looked into this as well. Apparently, you can't even read them without the proper computer equipment (wish they'd just hook up to a normal voltmeter.) Starting at about $250 - $300 right off the bat for that.

84redbronco
03-06-2010, 02:43 AM
It looks like I have the Duraspark II which would have vacuum advance adjustment capabilities in the CLOCKWISE direction versus counter clockwise on the distributor itself. I like the performance distributor. A little pricey, but if one expects the best performance/mileage output, sometimes you have to get the best parts that money can by. Thanks again 'not so' Abondoned Bronco.

Bigredmama
03-08-2010, 08:21 PM
Hey Abandoned..2 questions..what year 4.9 could I get those exhaust manifolds from and what kind of gas mileage are you getting from your 4brl set up?

AbandonedBronco
03-09-2010, 10:34 AM
It looks like I have the Duraspark II which would have vacuum advance adjustment capabilities in the CLOCKWISE direction versus counter clockwise on the distributor itself. I like the performance distributor. A little pricey, but if one expects the best performance/mileage output, sometimes you have to get the best parts that money can by. Thanks again 'not so' Abondoned Bronco.

Awesome on the Duraspark II. That should save a few headaches for the moment. Of course, sometimes it's better to find problems than not, because problems mean you can fix them. (Kinda like going to the doctor when you feel horrible and the doctor says you look as fit as a fiddle.)
Yeah, those distributors are a little pricey, but not really when you think about it. Stock dist. = $80, ignition module = $50, performance coil = $30. That's already $160. Doubling it to get them all in one perfectly tuned for peak performance for your engine really isn't too bad! But yes, it's still $320.


Hey Abandoned..2 questions..what year 4.9 could I get those exhaust manifolds from and what kind of gas mileage are you getting from your 4brl set up?

Hey Bigred, the EFI exhaust manifolds come from any fuel injected 87 to 96 4.9.
They're a little time consuming to remove because the intake on those is so much more involved than the carb model, but worth the trouble. Nothing serious, just lots of little nuts and bolts.

On my last trip, I got 15.6mpg @ 65mph. Still running a little rich, and it was 15 degrees out, so I'm hoping to be able to pull just a touch more. If I can get to 17 or 18, I'll be happy.

Bigredmama
03-10-2010, 02:24 PM
Any suggestions concerning the EFI manifold swap and keeping a carb warmer?..what did you do with the 4barrel?.(I've still got my 1brl.)

AbandonedBronco
03-10-2010, 02:29 PM
I had a plate made that fit the same shape as where the exhaust bolted to the intake. Then had two pipes plumbed into it and ran coolant through them. Have to seal off a few things or the fluid will come out the EGR and AIR pump holes, but it isn't too difficult. If you put one on, be sure the inside of the intake is clean, or all the carbon from years of exhaust will go into your coolant.

http://www.supermotors.net/getfile/717406/fullsize/081808185900.jpg

http://www.supermotors.net/getfile/717407/fullsize/120408174300.jpg

http://www.supermotors.net/getfile/717413/fullsize/img_1107.jpg

http://www.supermotors.net/getfile/717417/fullsize/img_1087.jpg

84redbronco
03-11-2010, 11:48 PM
Hey Abandoned, it's me again. I had a chance to dig into the Bronco a little more and found a few things. I decided to see if I could adjust the internals of the vacuum advance and found that it was already as far advanced clockwise as it would go. Since I am not currently having any issues-predetonation-I left it like it is. I also noticed that my choke flap was in the closed position-shouln't it be open after the engine has warmed up? I could push the flap open and it would stay open, but when I worked the throttle linkage, the flap would fall back to a closed position. I also noticed that for the electronic part of the choke, the negative WAS grounded to the body, but there was NO wire feeding the positive. I tried a jumper wire from the battery to see if I could get the flap to close-didn't work. I also noticed what looked like a vacuum port at the base of this. Should there be a hose going to this, what's it for, and where would the other end attach to. I didn't think the choke should remain closed at all times so I temporarily secured it in the open position. I didn't think I would need a choke,atleast for today since it had benn raining and the temperature outside was suppose to get up to 70 today. After doing this I decided to reset my two mixture screws at the base of the carb. I wound up with both screws about 1/8 further in clockwise than before I started. I did this by ear as I don't have a vacuum guage. This would be running less rich and help on gas mileage right?
The start-up to return to work was a LITTLE more difficult as I didn't have the choke to keep up the revs a little bit to get me from REVERSE to Drive, but it never stalled. Once in DRIVE/idling it seemed to be a little quieter than before. Also, before when I pulled out onto the highway it would seem to have an ever so slight skipping/surging/bogging halfway between the first to second shift-I did not notice that today. Also, further down the road, I nailed the throttle-I guess I was at a speed that didn't require the trans. to downshift-the engine pulled good with no noticable issues, but I did not take it to high in the RPMs-just full throttle from 40mph to about 55mph. Could the closed choke plate account for the surging/bogging, a sooty tailpipe(plugs look OK though), rich smell after a stop and sometimes irregular restarts when stopping at the store (flooding?), as well as hindering gas mileage? I need your input, on the whole choke dilemma especially, on how to get it running properly and what ill effects it would cause from running it closed the way it has been. Thanks.

84redbronco
03-12-2010, 08:34 AM
84redbronco again. I may be a bit confused as stupid as it might sound, but the choke flap I am referring to is the large single flap-not sure if this is over the primaries or secondaries-thats where my confusion lies. Also too I noticed on the other side of the carb, there are two bowls as well that have individual flaps the size of quarters/halfdollars. These flaps were closed for the most part as well and could not tell what operates them. Underneath these were two more similar size flaps that were almost closed as well and seemed to be somehow connected through linkage contact around the electric choke area. Have not done anything to alter the position on these yet. The lever on the outside of the carb to the two lower smaller flaps were kind of bent when I got the Bronco-just wondering if the electric choke closed off both the large flap AND the two lower smaller flaps when working properly. Please clarify which flaps cover which primaries/secondaries for future dumbasss me. Right now I'm just using the gas guage as a guage of gas mileage which I know is not the correct way. The correct way would be to start with a full tank and top it off each time. I know the old gas guage cannot be totally reliable for accuracy,but figured could be used as a half-assed estimator in the interim. I just figured I'm getting 5-8 right now-granted this does not fully take into account the recent changes made, but not very encouraging, but it seems to run rather well. HEEEEELP!

AbandonedBronco
03-12-2010, 11:03 AM
Hey 84Red,
I'm not familiar with that particular carb to know what all the little bits and parts that you're talking about are. Each one's a little different (although pics could definitely help.)
Either way though, if your choke isn't opening all the way, that can inhibit performance and gas mileage quite a bit. If it's not opening AT ALL like you're saying, that can really make it run crummy! When at idle and the engine cold, the choke should be open just a slit. When it's fully warmed up, that choke plate should be straight up and down allowing the most air in as possible. This is because the engine requires a much richer mixture when it's cold for combustion, so the plate closes to decrease how much air it's getting. Once it's warmed up, if the plate's still closed, it'll run rich and lack in power because it just can't get enough air in. Both quickly attribute to loss of power and poor gas mileage.
You'll want to hook a wire up to that positive on the choke. I think the battery is a bit too strong to hook up to the choke, it'll burn the element in the choke right up and you'll have to buy another one. This is what my manual says about finding a correct positive source: The positive wire should be secured to the positive (+) terminal on the choke cap, with the other end connected to an ignition activated
12V source. (Note: The ignition coil is not a 12 volt source after cranking, it is a 7-9V source after cranking.)

Before you do anything else with the carb, your first priority should be getting your choke operating properly. However, if you can't get it working, you'll want to secure it so that it's always OPEN. It'll suck driving it or getting it running when it's cold, but when it's warmed up is more important.

After it's fully warmed up, and the choke fully open, then start messing with the mixture screws and stuff. A vacuum gauge is pretty cheap, and I'd definitely recommend one, it's one of the best tuning tools you can get. :)

SLOFordtech
03-14-2010, 11:02 PM
a little off topic i have an 89 with a 300 I6 efi, and it makes a kinda small knocking noise but runs great plenty of power, oil pressure is good so im thinking maybe not worrying about it, alot of people told me they are bullet proof and tend to be noisy, but everyone i been in does not make this little knocking noise, sounds like bearings cause its low and seems to be happening at the engines rpm. made a big difference with thinker oil, but was louder while warming up, anyone think i got a problem or is it probably normal for a engine with mileage? any info would be great.

AbandonedBronco
03-15-2010, 11:10 AM
Hi SLOFordtech,
Completely wrong place for a question like this, as this is a technical writeup for aftermarket carb performance.
Best to start a new topic on this one and ask the general forum. Also check out http://www.fordsix.com and http://www.ford-trucks.com/forums/forum52 for more 300/4.9 based info.

84redbronco
03-15-2010, 09:48 PM
Abandoned,
I did a little research on Carter carbs after my last reply, wasn't that easy. I still did not find my particular carb in searching, not even using the numbers stamped on the carb. I did however find that mine is basically called a Carter AFB and from what I can tell, they do not make them anymore. Essentially, Edelbrock now has the Carter patent rights and any similation to mine would be an Edlebrock AFB carb. In looking at electric choke operation in general, I found, like you said, that positive power should come from a keyed power source. When I was just using the battery, I only made contact for just a second or two because I did not see anything happening, but what I found out from reading is that it takes more than a second or two (30 sec. to 1 min. actually)for the bi-metallic element inside to heat up and pull the choke OPEN for normal driving after the closed choke is used to assist in cold cranking. I guess I could check resistance on the +/- to see if there is a break inside first. You can also check the adjustment by rotating the electric choke housing so that the choke is ALMOST closed with an ambient temp. around 65-70 degrees at time of adjustment. Also, the vacuum fitting on the choke housing that I mentioned earlier might be something that would say need to be hooked to an EGR port to aid the keyed power source in heating up the element or as a back-up to the keyed power source. Some chokes even have coolant running through them. From what I gather, they could have one or all three ways to aid in heating this element up in order to open the choke once the vehicle is started. As far as the vacuum gauge goes, they are cheap enough that I need to go ahead and just get one. One other note, I did hear a slight ping at one point in accelerating today. I am assuming this is related to the VACUUM advance. Maybe I was able to get a little more out of the vacuum advance than I thought afterall. Anyhow, it wasn't bad enough to warrant re-adjustment of the vacuum advance just yet, but I will keep an ear out for it. Also, my earlier reference to the other small butterfly flaps inside the carb, I think I have found through searching that these are my VACUUM operated secondaries. In addition, I found that mine may not have a powervalve such as yours, but actually have power valve needles that are accessible from the top of the carb located under a smaller than dime-sized cover plate on either side of the the choke flap.

AbandonedBronco
03-16-2010, 06:04 PM
Glad you found some info on the Carter 4bbl! If you don't understand the dynamics of your carb and how it ticks, all you can do is hope it's working right. That sucks.

So the choke hasn't been opening at all? If neither of your choke warm-ups are hooked up, I have a pretty good guess why you're getting horrible mileage. Yeah, a quick touch of the key won't open the element up, it takes a little bit of time. There's a coiled spring in there that expands as it heats. The stock 1bbl on mine had both. The electric would slowly warm it, and then it was helped by a tube that came up from the manifold that supplied warm air. It worked pretty well.

Get the choke opening and closing properly, then start in on the advance, and I imagine you'll be pretty pleased with the changes you'll notice in the engine. Don't know a drop of info about tuning Edelbrock's (if your Carter is similar), so you're on your own on that one. But when I started in on the Holley, I knew absolutely nothing (only last year), so just dive in.

84redbronco
03-16-2010, 10:50 PM
Where exactly does your heating tube lead from now with your current set-up, provided you have an electric choke now on your Holley or where would it come from now given you are running a different set-up now and yet our current set-ups are similar yet different in ways. A pic would help,as well as a possible wire already existing within the engine bay that I can use or tap into for power to the heating element. I did have my choke rigged in the open position and some difficulty on cold starts, but was willing to sacrifice that for any improved mileage until I could dig into it. I decided to undo the rig on a cold morning to help with the start and deal with the worse mileage only temporary, hopefully forcing me to dig into it again, but it is still difficult to start. When un-did my rigging on the choke it was with the air filter on. Who knows, the choke may be stuck open now. I will have to dig into this again. Hopefully I will have some useful info. from your end by then with which I can use to atleast improve on my current situation.

AbandonedBronco
03-17-2010, 12:13 PM
On the Holley I have, it only has an electric choke and that's it. I'll have to look and see where the wire comes from, but it's the stock wire for the electric choke on the old 1bbl. Yours either has it and it's tucked away, out of sight, or it's been snipped off and removed. If you don't have one, get a voltmeter and find a wire that's only on when the key's on and just splice a small gauge wire into it and run it up to the carb. If your choke is like most I've seen, it'll just have a tab on the positive, and you'll need to put one of these on the end of the wire: http://rocky.digikey.com/weblib/Molex/Web%20Photos/19002-0005.jpg

I have seen where you can buy heat tubing for chokes. It's pretty soft metal, and you can just wrap it around the exhaust manifold or headers, and the air going up through it to the choke will be hot. However, the electric choke should be sufficient to take care of the whole thing, the heat tube just helps. If the element in the choke is still good, and you get the electric wire hooked up to it, you should be alright.

84redbronco
03-19-2010, 11:25 PM
I checked the continuity across the +/- on the choke and the meter said it was bad. I decided to hook power up to it any way(negative already grounded). I found a keyed source on one of the small posts on the starter relay which is mounted on the passenger side fender wall. Some where I thought I read not to get power from here, but I thought it was safe enough since it was a keyed source of power. I left the ignition key on while I worked on other things and checked it later and the choke still did not move open and the housing was not warm. Oh well, I left it hooked up anyway. Checked it this morning before running an errand-choke still closed as it should be. Started and ran fine-good power and response. I came back and unloaded some stuff and the battery did not have enough juice to fire the engine. Thought it might have been due to the rear window and thought maybe the switch might still be in slight operation mode, but it was in the neutral position so I just attributed the battery drain to the addition of the new power supply since I have seen this happen before when there was a short or bad ground, just not this quick. Choke still closed with engine at operating temp.- removed power supply wire. I might have an alternator problem that takes a while to drain the battery since I only go short distances. I'm currently using my deep cell marine battery which I know is good and had installed it when I put on the new starter and relay and could put the old battery on charge to see if it was any good or not and might have contributed to any of my prior starter/relay issues. Gas mileage appears to be doing OK, won't know for sure until end of next week. I'm atleast hoping to get better than the 8 or worse that I got last time-OUCH! If it is better, I will attribute it to the prior adjustments made to the mechanical and vacuum advance-topped out there I believe. On a side note, when I was working on the choke, I was taking the linkage to full throttle with the engine off to examine the operations of carb and linkage and about 2 out of the 10 times I did this, I noticed a trickle of gas come out somewhere around the area of the linkage on/around the electric choke side of the carburator. Is this normal considering what I was doing or is this a sign of something I need to have checked out or rebuilt?

84redbronco
03-22-2010, 12:12 AM
I just happened to look at Edelbrock's on-line store and my Carter Competition Series carb that I have bares an exact resemblance to Edelbrock's AVS Performer Series Carb. Not sure if I have a 500 cfm or 600cfm, but I think I have a 600cfm because the 500 cfm w/electric choke that is offered is calibrated for dual quad applications or if it was for single applications it had a manual choke. Anyhow, it's not anywhere close to 390cfm. I was looking at a new choke, rebuild kit, etc.(if that would even work on my Carter) and I could double the cash and get a shiny new looking remanufactured one for about $230. I'm very tempted since my linkage is slightly bent, sticking, possibly leaking fuel either inside or outside, choke doesn't work etc. Just piece of mind with a like new, calibrated, bolt on piece I guess. I would probably go back with this same design even though the cfm may be high due to the fact that there are no power valves to blow and the gas does not have to be drained or carb removed to work on it. 600 cfm might sound like to much, but 500 and 600 are recommended for cubic inches around 300. The 600 cfm may be for getting the most out of a 302 high performance engine, but I don't plan on getting max power out of my 300. I guess the carb has the capability if I need it, but I don't think it will necessarily hurt either by not doing so. Any thoughts on that one?

AbandonedBronco
03-22-2010, 11:51 AM
Hey 84, it sounds like you have a fuel leak around the throttle linkage. There shouldn't be any reason for fuel to be coming out anywhere except inside the carb.
Also, if you were certain you were getting a current to the choke while the engine was running, and it wasn't opening, it sounds like the element inside might be shot. They can be replaced, but it comes down to whether or not you can find one for that carb.
If it were me, and you have the extra money, I'd definitely go with the new carb. You can rebuild the one you have if you can find the kits for it, but who knows what other parts are worn out, like throttle shafts and stuff, that aren't fixable with a kit. Especially for $230. One of the main reasons I went with the Holley 390 on mine is because they still make them. You can order parts for it anywhere, instead of scouring flea markets and swap meets hoping you can find some 20 year old kit someone had lying around in their garage. It's a nice piece of mind.
As far as the Power Valves go in Holleys, they have had blowout protection in them for a decade or more. PV blowout is something you only have to deal with in much older carbs, and even those can have the protection added. Pretty much a non-issue anymore. Draining the fuel to change jets can be a little annoying.

500 - 600 CFM can be a little big for the 300. General formula for size is ((Engine C.I. * Max RPM) / 3456).
(300 * 4500) / 3456 = 390.625. Even then, 4500 RPMs is still a little high, although doable.
A 302 can rev quite a bit higher than the 300, which is why they like a much bigger carb. (302 * 5500 / 3456) = 480
That's also on the high end. Usually reduce that by about 10 - 15% for more stock engines (no head porting, stock cam, etc), which makes 600 pretty overkill. However, that's where vacuum secondaries come in, since you can make them open later. That way you can put a bigger carb on, even though you won't use it all.

On the other hand, I do know a few guys who run Edelbrocks and like them. I'm still not 100% sold on my 390, so if you put it on, like it, get great gas mileage, etc. be sure to share! I just might follow in your footsteps.

84redbronco
03-23-2010, 12:16 PM
Appreciate your input on this, See, that's what this site is all about-sharing info. with others-if you don't mind sharing all the hell one went through-so that someone can make their own decision on info. gathered or advice given. I forgot about the whole formula thing-almost swayed to new Holley 390 on that note, but I may decide to still go with a new Edelbrock. I have another project car that I may put a small block v-8 in and if for some reason I let the Bronco go, I can atleast use the new one on the project and throw the old one back on the Bronco. I need to look better for the carb. identification number to see if I have a 500 or 600 cfm. Do you think I am losing any mileage from the bigger carb or because it is bigger, I just may not get into the secondaries that much? Either way, I will let you know when that time comes. The new ones that I have seen for my single electric choke application are jetted for performance-I will have to re-jet for economy if purchasing new. The internet can be so cool!!!

mrob252
03-26-2010, 12:40 PM
hey guys, first time poster here.

i've got an old 85 4.9 l6 that my dad gave me a while ago. it's been sitting around the backyard, and i've been running it occasionally the past few years just driving it around on the farm.

i've been doing some research on it as i want to fix it up a tad bit and make it into a little mud/fun truck. i've been reading a lot on this site and i've found that i want to do the duraspark II swap and go ahead and convert it to something that will be MUCH easier to maintain and work on. the problem is i CANT find a full write up or a full article on what exactly to do...

i've used the search feature a few times with no exact results. sorry to threadjack but i'm just hoping one of you guys might be able to point me in the right direction.

thanks.

AbandonedBronco
03-26-2010, 12:48 PM
Hey mrob252. What is it exactly you're wanting to do? Are you looking at just fixing it up, or are you looking at upgrading? If upgrading, this particular thread's the one to check out. But if you're just looking to get rid of your feedback carb setup and go with a DuraSpark II, you probably won't find a lot of info on this site, since 300s weren't super common in Broncos.

For general stuff like that, definitely check out:

Http://www.fordsix.com/
and
http://www.ford-trucks.com/forums/forum52

You'll find all the info on that stuff and more on the I6 in those forums as they're engine specific.

Bet of luck!

mrob252
03-26-2010, 12:56 PM
thanks abandonedbronco.

i'm looking to just get rid of the feedback carb setup and go to the old style carb/dizzy system. i had an engine fire a few years back and it burned up a lot of the wiring under the hood. now it runs horrible, when it runs at all. i'm not looking to upgrade and turn it into a beast or anything. just trying to make it more reliable and easier to work on for the applications i need it for, which is really just driving around the farm doing stuff or picking up a deer i shot.

thanks for the help though. i'll check out those sites and see what i can find. i didn't know the 300 was so rare in the broncos.

AbandonedBronco
03-26-2010, 01:05 PM
Some information that should get you moving forward.

http://www.ford-trucks.com/forums/906647-duraspark-ii-questions.html
http://www.classicinlines.com/DSII_swap.asp

The DSII swap will make your engine much happier and run way better. Should be fun.
I think the main reason they're less common in Broncos is because most didn't get Broncos for "working trucks", which is what the 300 was great for. People got them for power, performance, off-roading, etc., so the V8 package was very common. I think in 93 or so, they stopped offering the I6 in Broncos altogether, even though it was offered in trucks for a few more years. That and the 78/79 Bronco only offered the 351 or a 400 V8s with no I6 at all either.

I think we did a poll a little while back and it was about 5% 300, 45% 302, 50% 351.

84redbronco
03-29-2010, 09:26 PM
Hey Abandoned,
I finally found some information on-line that gave me info. on the size of the Carter in reference to the casting no. on the carb itself. It appears that I have a 500 cfm-I can live with that and would probably go with an Edelbrock 500 cfm Performer if I were to go with a new one. I'll still post later with recent mileage numbers.

AbandonedBronco
03-30-2010, 10:51 AM
Was looking at a site while ordering some jets and noticed this link down in the corner. Was thinking, "Hey, I know someone who's got a Carter Competition 4bbl..."

http://allcarbs.com/tech.php?art=17

Not a LOT of info, but it tells all the original parts, sizes, etc. May help if you're intending to keep it.

84redbronco
03-30-2010, 09:56 PM
Small world- that just happens to be the exact site that I got the info. from to i.d. my carb. I saved it just in case for parts, manuals, etc. I made a copy of this page and put it in the glove box for whoever might would need it. Thanks.

nrbigbuck
03-31-2010, 09:59 PM
Just about got all the parts to swap intake/exhaust and carb on my '80 bronco with 300. I am really leaning towards holley 470 truck avenger. anyone use this carb yet on 300?

nuckinfutz
04-21-2010, 09:13 PM
Small world- that just happens to be the exact site that I got the info. from to i.d. my carb. I saved it just in case for parts, manuals, etc. I made a copy of this page and put it in the glove box for whoever might would need it. Thanks.

From everything ive been reading from you on that AFB you have go with a a smaller carb bigger isnot always better..The 500 cfm is to much of a opening on a IL6 for velocity needed ...Like a McDonalds straw versus a BK staw ...Wow a weird analogy..
the choke + and - is just that it will add pressure + to butterfly closing and holding it there where - reduces the pressure thus making it easier to open...the heating element if in the full + position cannot expand enough to let the choke open..try going to the - side and see what it does...loosen the screws and rotate it should have arrows..
I recomend the 390 as does clifford and offey for a 6 ...i cannot wait till i get the full kit from Summit ...Great Write up Props..

Bigredmama
06-14-2010, 03:19 PM
Hey Abandoned..thought I'd run this one by ya..as discussed a few months ago I swaped out that cluster..worked great..my last camping trip..(Memorial day weekend)..subjected the truck to some severly tramatic roads..(wash board)..head lights flickeriing and the whole bit..got back home w/o any problems except that the fuse box rattled loose from its mounting screws..hung it witha zip for the time being..2 wks later..yesterday..drove the truck and noticed that the tach is now off..(around300-500) rpms..what would cause this?..as a side question..if my flap on that crappy 1 barrel is staying closed..how do I fix this..(can't wait til next year to do the intake and carb upgrade..)

AbandonedBronco
06-14-2010, 03:36 PM
Hey Abandoned..thought I'd run this one by ya..as discussed a few months ago I swaped out that cluster..worked great..my last camping trip..(Memorial day weekend)..subjected the truck to some severly tramatic roads..(wash board)..head lights flickeriing and the whole bit..got back home w/o any problems except that the fuse box rattled loose from its mounting screws..hung it witha zip for the time being..2 wks later..yesterday..drove the truck and noticed that the tach is now off..(around300-500) rpms..what would cause this?..as a side question..if my flap on that crappy 1 barrel is staying closed..how do I fix this..(can't wait til next year to do the intake and carb upgrade..)

Hey Bigred,
The tach would probably be a question that'd be better posted in the general tech session. Got no idea on that one! May want to check connections on the coil and such. Or maybe the actual needle slipped? Dunno.

As for the flap on the 1bbl, are you meaning the choke butterfly directly on the top? If it's not opening, your choke isn't working and as a result you'll get horrible gas mileage and low power.

4x4300Bronco
06-24-2010, 11:03 PM
Abandoned, I've been reading this thread for a while now, decided it was time to finally register. I'm about to do the same conversion you did, with the Holley 390 and Offy dual port. Mine's going to be on an '85 Bronco. My biggest concern right now is the throttle cable bracket. I have very limited access to a drill press, grinder, etc. and I'll have to drive 20 mins away from where I'll be working on my Bronco, to get to those tools. Does anyone make a bracket for this conversion? If it's half way reasonably priced, it'd be worth it to me to not have to drive back and forth. Thanks!

AbandonedBronco
06-25-2010, 12:52 AM
Hey 4x4 300,
Look up the company Lokar. They make a lot of different types of throttle brackets. I know several that use their bracket when they convert their 300 to a 4bbl, but I'm not sure which one. Does exist though. Maybe shoot Lokar customer service an email and ask which one to use.

For the cable itself, I used my stock for a while but it sucked, so I got a $20 job at Schucks that works really nice. Just a standard universal aftermarket throttle cable.



On a side note, I'd highly recommend a Mr. Gasket #260 for the exhaust / intake gasket. It seals up very nicely. May have to order one online if you can't find it locally.

4x4300Bronco
06-25-2010, 08:37 PM
Great call on that, Abandoned. I have one on the way now. As fate would have it, I have that very gasket sitting next to my manifold and carb as we speak - er - as I type. I will indeed have to use a different throttle cable with this bracket, but since I just noticed the one that's on there is starting to fray anyway, no big deal. By the way, the part number for that bracket from Lokar is SRK-4000 and it's about $24.00 from Summit. Thanks for your help, I'll let ya know how it turns out.

AbandonedBronco
06-28-2010, 03:22 PM
Awesome to know, since I've never been 100% pleased with my home made one. It always gets the job done and never causes any problems (guess I shouldn't complain and consider myself successful), but it'd be nice to actually have a real bracket in there that I know is made for it. :D

Be sure to post up pics of your install!

tlg013
02-21-2011, 05:14 PM
Hey I know I'm pulling up an old thread, but I just did the same thing to a buddies 300 and we were wondering what your base timing was set at and what your carb jets were set at etc.?? Thanks.

AbandonedBronco
02-21-2011, 05:23 PM
Heya,

The base timing was around 10 - 12, although I usually set it with a vacuum gauge so am not 100% sure what the actual number was.
If you don't know how to do that, it's pretty simple. Disconnect the vacuum advance and plug it so there's no leaks.
Connect a vacuum gauge to direct manifold vacuum.
At idle, advance the distributor until the vacuum on the gauge no longer increases.
Back the timing down until the vacuum drops to 2hg below the highest reading. (For example, if you could get the vacuum up to around 20, back it down to 18)
Reconnect the vacuum advance.

That'd about the best base timing you can get, since it takes into account all the changes you've done, as well as your elevation and such.


On the jets, I leaned it out a bit to around a 48 or so. Then increased the accelerator pump squirter to a 35.
Those may change on yours depending on gearing and elevation. Higher elevations require smaller jets due to less oxygen in the air, and taller gears (mine's a 3.00) can require larger accelerator squirters to get them moving.

Hope that helps.

tlg013
02-22-2011, 09:01 PM
Yep helps a bunch! We are at 100 ft elevation around the coast here. Not sure on the gears but its a 86 f-150 with I think a T-18 tranny 2x4.

'84Bro
01-10-2012, 02:12 PM
Hey Abandoned, Really appreciate your write up on this. Last Nov. I purchased a 1984 Bronco Custom with a rebuilt 300 IL6 after reading this write up. Have just completed the Offy DP intake and 390 holly carb ( each new) upgrade and in the future the EFI exhaust swap (will for sure use ur write up). Found a cable for my kickdown from summit cause I have a C-6 tranny. My PO had removed all the emissions gear and I remove all the excess wires and vac line along w/it. Reading through the threads I concluded that I have a DSII Dizzy, had to fix a few bad wiring splice that had me replacing a coil, Started relay, and ignition mod before I found the bad splice to the dizzy. Major headache but learned a lot and the tech threads were very helpful. Haven’t yet began to tune the carb and timing, its next. (gotta work and feed the Bronco beast!) Anyway a few questions:

1) I read where you tuned the timing with a Vac Gage, Do you have a Write up on that and can you tune the Carb in the same manor?
2) Is there any way to tell if a distributor recurve kit has already be installed on my dizzy? Is there a Write up on the install?
3) Do I need to regap my plugs, open or close?
4) Do you have a MAF or P# on the 4bbl carb heated spacer?
5) Where did you get the Manifold studs?

As soon as I can I’ll post some pics of mine.
Thanks, ‘84Bro.

AbandonedBronco
01-10-2012, 02:49 PM
Hey Abandoned, Really appreciate your write up on this. Last Nov. I purchased a 1984 Bronco Custom with a rebuilt 300 IL6 after reading this write up. Have just completed the Offy DP intake and 390 holly carb ( each new) upgrade and in the future the EFI exhaust swap (will for sure use ur write up). Found a cable for my kickdown from summit cause I have a C-6 tranny. My PO had removed all the emissions gear and I remove all the excess wires and vac line along w/it. Reading through the threads I concluded that I have a DSII Dizzy, had to fix a few bad wiring splice that had me replacing a coil, Started relay, and ignition mod before I found the bad splice to the dizzy. Major headache but learned a lot and the tech threads were very helpful. Haven’t yet began to tune the carb and timing, its next. (gotta work and feed the Bronco beast!)


Heya '84Bro,
Glad the writeup was helpful!

That's cool you already have the DSII dizzy.
To quickly check:

Duraspark II dizzy:

http://image.mustangmonthly.com/f/miscellaneous/durable-duraspark-distributor/9523865/performance-distributors-duraspark-distributor.jpg

It'll have the vacuum advance canister on it vs. the SPOUT connection. The SPOUT connection is a big electrical plug in, but doesn't hang off by wires like the DSII one does. It's more solidly connected to the body. Plus, you'll have an ignition module on the wheel well.



Anyway a few questions:


1) I read where you tuned the timing with a Vac Gage, Do you have a Write up on that and can you tune the Carb in the same manor?

I'm sure there is one, but the process is really simple. For both, be sure the engine is fully warmed up.

1. Connect a vacuum gauge to direct manifold vacuum. Generally, a port on the manifold itself, or the port on the Holley 390 that's on the base plate (not on the metering block).
2. Disconnect the vacuum advance hose to the distributor and cap off the vacuum line.
3. Loosen and rotate the distributor (advancing timing) until you get the MAXIMUM vacuum possible. Now, rotate the distributor (retarding timing) until the vacuum reads around 2 less than the maximum number you reached. So, if you rotate the distributor and it peaks out at around 20, back it down to 18.
4. Reconnect the vacuum advance hose.

Your timing is set.


As far as the carb goes, you can set the idle with a vacuum gauge.

To set the idle:

1. With the engine off, turn both idle mixture screws in all the way until they barely bottom out. Don't tighten them or you'll damage them.
2. Back both screws out 1 1/2 turns. This is a good base to start from.
3. Start the engine.
4. Slowly turn each idle mixture screw until they get the highest vacuum reading possible. Just keep tweaking them until the vacuum is as high as you can possibly get it. The finer tuning you do to zero it in (even little 1/16 tweaks), the better.
5. If the idle RPMs decrease or increase, reset the idle. You want it around 700 or so. If you don't have a tach, you'll have to set this by ear. If you have to reset the idle speed, redo step 4.
6. Balance the two idle screws. Meaning, if one screw is out 2 turns and the other is out 1 1/2 turns, set them both to 1 3/4.

Once you're done with the idle, recheck the timing. If there is a significant change, redo the idle mixture. If the idle mixture changes a lot, redo the timing. Etc. etc. until no more changes need to be made. It should be purring like a kitten.

If, after all that, though, your vacuum is low, such as around 14 - 16, you may have other problems (most likely vacuum leaks). It should be around 18 - 20, especially with a fresh rebuild.


2) Is there any way to tell if a distributor recurve kit has already be installed on my dizzy? Is there a Write up on the install?

I don't think there is a way to tell if it's already been recurved. About all you do is change the internal springs and bend the mounting tabs they're on. Nothing would be visually noticeable.

Here's a writeup though: http://reincarnation-automotive.com/Duraspark_distributor_recurve_instructions_index.h tml


3) Do I need to regap my plugs, open or close?

This'll depend more on your ignition. If you have a hotter ignition, such as a performance coil or module, you can definitely open them up some. I think 0.055 is the max with a good, hot ignition.


4) Do you have a MAF or P# on the 4bbl carb heated spacer?

There's two options for this. One is the underside heated plate, which you can get at http://www.truckmeblue.com, or make your own.
As for the heated spacer I have, you can get them on ebay or from a late sixties Ford Galaxy or T-Bird with a 390 V8. Just be sure to fill the big opening on the side or you'll have a massive air leak. Best way I've found is to just completely fill it with JB Weld and then take the plate down and have it resurfaced back to flat.

To find them on ebay:
Search for "Carburetor spacer"
Set the search to "used" only.
Look through the pictures until you see a 4bbl spacer that has a pipe coming out of both sides.

They're pretty easy to spot.


5) Where did you get the Manifold studs?

I got mine at a local nuts and bolts store. Don't get them at a place like Ace Hardware unless you have to. They'll have them, but they charge a lot more for them. Those little specialty industrial places will usually have a lot better deal. Also, get Grade 8 hardened steel. Don't cheap out, or they'll snap on you. Been there.
That truckmeblue.com site has the studs as well.



Best of luck! Hope all that helps.

Handy_andy_cv64
01-10-2012, 09:59 PM
Yo, AB, good to see you back on. Got any current operational info, such as MPG, breakdowns you've had to fix, etc.?

AbandonedBronco
01-11-2012, 03:55 PM
So far it's been an extremely reliable setup. I've said it many times, but Ford would have had a winner on their hands if they'd released it from the factory with an H.O. configuration.

It moves great, too. The upgrade pretty much removes the downfalls of the 300 with being slow.


I changed out my carb for a 600 cfm due to my inability to get my 390 dialed in. Just couldn't get it to do it. I'm thinking I had a bad carb since I know quite a few others who've had great success with it.
However, with the 600, I'm getting around 10 - 13mpg in town, depending on summer/winter. Highway I'm getting around 15 - 18, depending, again.

Handy_andy_cv64
01-11-2012, 10:05 PM
Yeah, I think too many old-timers running the powertrain engineering department at that time...their thinking just was too twisted between the suits, outmoded ideas and the government.

AbandonedBronco
01-12-2012, 10:05 AM
There's a guy over on Fordsix.com who's a retired Ford engineer. His favorite engine is the 300. (In fact, he has one in his dragstrip car.)

He said much of it had to do with emissions and such, but a great deal was simply that the V8 brought in money. It was a "performance upgrade". Why would anyone spend several thousand more on a truck to buy a V8 when the I6 had the same HP and torque, lasted longer, and way better gas mileage?

Granted, a V8 can be built higher and easier than an I6, but when emissions are concerned, you can only go so far.

'84Bro
02-15-2012, 05:16 PM
Hey AbBro, I thought I had left a reply to ur comment on my questions, anyway, still trying to figure out this whole how to post pics. I have settled out my upgrade and am still fiddling with tuning it cause I think I can make it better, getting about 12mpg but I attribute most of that to the C-6 tranny...still have the kick down cable to install from summit but thanks for your reply was most helpful.
As soon as I get the pic thing figured out I'll throw some up.
Peace out...

AbandonedBronco
02-15-2012, 05:29 PM
Heya 84Bro,

Is that 12mpg on the interstate or around town?

Yeah, the tuning and tweaking is where all the fun (and frustration comes in!)

For pics, the best way I've found is to either put them on Photobucket.com or SuperMotors.net. Both give you free accounts, and then when you upload them there, you can copy the link they give you for the picture and paste it here. Put an www.link.com/pic.jpg around the link and it'll pop up in the forum. :D

187racing
03-02-2012, 01:33 AM
I've had/built a few broncos with the 300, i've had really good luck with all of them. Last one had a clifford intake with a small schneider cam and a ported and shaved head. It would whip the new for 96 vortec chevys with 33's and got 19 hwy at 80 mph with no overdrive and 4.10's. I just picked up an 80 and have already swapped the crappy stock exhaust manifold for the later efi manifolds (last one had a clifford header), built a custom dual 2 inch into 3 inch single exhaust, and am saving up for another clifford intake and some sort of 4 bbl carb. I just installed and tuned a 470 cfm truck avenger on a friend's cj7 with great results and am leaning toward that at the moment. It fired right up and took minimal tuning to get it running right (and passing smog). when i get everything on and dialed in, i'll post back with results........

'84Bro
03-05-2012, 01:05 PM
Heya 84Bro,

Is that 12mpg on the interstate or around town?

Its a combo of both, about 50/50 on a 35 mile trip oneway.

Yeah, the tuning and tweaking is where all the fun (and frustration comes in!)

True but, the more I tweak it the better it runs...so, I'm a tweaker...

For pics, the best way I've found is to either put them on Photobucket.com or SuperMotors.net. Both give you free accounts, and then when you upload them there, you can copy the link they give you for the picture and paste it here. Put an www.link.com/pic.jpg around the link and it'll pop up in the forum. :D

Thanks for the photo info.
'84Bro.

AbandonedBronco
03-05-2012, 04:31 PM
I've had/built a few broncos with the 300, i've had really good luck with all of them. Last one had a clifford intake with a small schneider cam and a ported and shaved head. It would whip the new for 96 vortec chevys with 33's and got 19 hwy at 80 mph with no overdrive and 4.10's. I just picked up an 80 and have already swapped the crappy stock exhaust manifold for the later efi manifolds (last one had a clifford header), built a custom dual 2 inch into 3 inch single exhaust, and am saving up for another clifford intake and some sort of 4 bbl carb. I just installed and tuned a 470 cfm truck avenger on a friend's cj7 with great results and am leaning toward that at the moment. It fired right up and took minimal tuning to get it running right (and passing smog). when i get everything on and dialed in, i'll post back with results........

Sounds like you definitely know what you're doing when it comes to this type of upgrade!

However, I gotta say, getting 19mpg at 80mph, no overdrive, and 4.10s is counter intuitive to most anything I've ever heard of when it comes to getting good gas mileage with these. Not saying it's not true, but after discussing these engines along with these popular upgrades for several years now, you're the first to ever claim such numbers with that type of setup.

Wouldn't that put you around 3350 RPMs on the interstate? That seems really high for optimal gas mileage.

What do you aim for to achieve high mpg? AFR? RPMs? What size carburetor?

20sNaRanger
04-05-2012, 02:02 PM
So far I've been really pleased with the gas mileage the Holley 600 is giving me around town.

The 1bbl was giving me around 7 - 9 around town by the time I pulled it off (it's only real strength was highway mileage). It USED to get way better, like 15 or so, but it hated 10% ethanol gas. When that started to become the norm, the gas mileage was cut in half.

The Holley 390 was averaging around 10 - 12.

So far, with the Holley 600, I've been averaging around 12 - 14 around town.


My highway mileage has been considerably better as well, but I haven't done enough trips to really get a good estimate.

The Holley 390 was terrible on highway mileage. I would get anywhere from 8 - 13 on the highway.

The Holley 600 has averaged around 14 - 18 depending on the temperature outside, headwind, etc. Exceptionally better.

I'll be curious what you get.

I'm considering on getting some hooker shorties to put on there as well...but I figured that I'd do one thing at a time. :thumbup

I have a question for you AB. That bracket you and your brother did...can you elaborate more on that? I'm not getting a visual in my head as to what you made that for.

AbandonedBronco
04-05-2012, 02:08 PM
The only thing my brother and I did was this heat plate. Is that what you're referring to?

http://www.supermotors.net/getfile/717407/fullsize/120408174300.jpg

http://www.supermotors.net/getfile/842666/fullsize/img_3246.jpg


It bolts to the underside of the intake. Then, coolant flows through the cavity that's in there and heats it up. It takes the place of the stock heat riser.

Without it, the intake floor is cold, which on a carb'd vehicle causes bogs and hesitations that you can't tune out.

AbandonedBronco
04-05-2012, 03:47 PM
You probably won't find much on it online. It's a very specific application, which is aftermarket straight six engines where the stock heat riser's been removed. Maybe I4s as well. V6s and V8s don't work that way since the intake sits above the block.

There's some info over on ford-trucks.com (http://www.ford-trucks.com/forums/forum52) but it'll be mostly pictures, descriptions, and why they're helpful.

To make one, take down the stock gasket that goes in between the intake/exhaust manifold to a machine shop and have them punch out a piece of plate steel about 1/4" thick and have them drill and tap two pipe thread holes into it. Then, go get the pipes from a plumbing store. If you have to means, weld them all together so all the seams are tight. You should be good to go.

Use some make-it-yourself water-proof gasket and seal it up really well. Indian Head Gasket Shellac did the trick for me. :)

AbandonedBronco
04-05-2012, 03:48 PM
When I throw on the EFI exhaust manifolds, I think I am gonna try to hook up the EGR. Has anyone had luck with this? From what I can tell it's just a simple tube. Or should I just cap them off?

It's doable, for sure, but I've never done it.
EGRs are a good thing, and can help with both performance and mileage, so it's certainly worth looking in to.

Are you sticking with the 1bbl? If so, about all you'd need to do is come up with a flexible pipe that can go into the rear EFI manifold. It has an EGR pipe threading in it already. Just be sure to pick a pipe that can withstand exhaust heat.

If you go with a 4bbl, it's much, much more difficult, since there's no provision for the EGR valve to bolt onto.

AbandonedBronco
04-05-2012, 04:02 PM
Yeah, I think that's a pretty tall order since most any application with an EGR has a special, factory machined manifold spacer that the valve bolts onto. The idea is simple, but you'd have to have some decent tools and fabrication skills to pull it off.

AbandonedBronco
04-05-2012, 04:22 PM
I found some steel pipe end caps down at a plumbing supply store that fit perfectly.
I took my EFI manifold in with me and went through them until I matched one up.

FordsForeverEric
10-22-2012, 10:56 PM
Great write up!

I just bought myself an Offy intake off Craigslist for $70 as I'm planning on swapping my 87 to carb

I was wondering if you would now where I could find dimensions for that adapter plate for a 4 brrl? I didn't get one with it and I would like to make one since I'm in college to be a machinist and have CNC mills that I can use :toothless

Most that I've read about swapping from EFI to carb was very negetive, but I'm a total noob to wiring and EFI stuff, not to mention my engine bay looks like an old birds nest of shitty wiring lol Its going to be a trail rig and play toy once I get out of school, so its probably going to get a switch panel, MSD or HEI ignition, and the least amount of wiring as possible. I'm still far off from doing the conversion, I'm too broke and its still my daily driver, but I'm sure I'll have a ton of questions for you down the road.

Any advice is appreciated :beer

AbandonedBronco
10-23-2012, 12:00 PM
Hi Eric!

I would think on that plate that you could either just buy a cheap 4bbl carb spacer off ebay, or just use your Offy intake as a template. If you're going to machine it yourself, make it hollow inside with an in and out port for coolant. The extra heat helps. :)

Most people do advice against going from EFI to carb. EFI has so much more drivability, especially in cold weather and altitude changes. But, unlike the 5.0 and 5.8, the 4.9's EFI really isn't upgradeable. So, if you want more power, you almost need to go to a carb setup.

FordsForeverEric
10-23-2012, 02:39 PM
Yeah I was thinking of using the intake for a template, but the adapter plate has those 4 main holes in the center? I don't know the size or the exact locations of those? I was thinking I could just buy the gasket off Summit for $2 and use it for a template. I'll have to look at the intake a little closer and see how I could make the coolant flow through the spacer... not really sure how that works

FordsForeverEric
10-23-2012, 02:42 PM
I'm wanting the adapter to look like this correct?

http://www.cliffordperformance.net/Merchant2/merchant.mvc?Screen=PROD&Store_Code=CP&Product_Code=7-F&Category_Code=F300

AbandonedBronco
10-23-2012, 03:05 PM
If you're going with a 4bbl carburetor, you could use the carburetor itself as a template. Measure the barrels with a micrometer, as well as bolt spacing, etc. That way, your plate would be perfectly matched with it for best air flow.

But, yeah, that'd be the plate to copy.

Someone had an idea of making their own heated plate by taking a normal spacer (like the one in your link) and drilling drilling through it:

http://i75.photobucket.com/albums/i291/sandmann999/HeatPlate.jpg

Kinda like that. If you did it, you could machine the plate, drill the holes for the barrels, and then drill across where the dotted lines are. Fill/put plugs where the Xs are, and then run two tubes out of it to slide a hose over. That way, coolant will run in one side and out the other, heating it up.

Heat under the carb, or even more importantly, to the underside of the intake, is very important to drivability in a carb'd engine.

The other one commonly made is a flat plate that bolts to the underside and has pipes coming in/going out of it. I think I have some pics of mine in this thread.

FordsForeverEric
10-23-2012, 03:18 PM
I guess I should get a carb first then lol

I'm sitting here looking at my intake and realized that its not the same as yours... I got the C series single port http://www.summitracing.com/parts/OFY-6227C/ while yours is dual port? what difference does this make? does that change how I should make an adapter?

I get what your saying about running the coolant through it... I'm gonna have to work on that, shouldn't be too hard to do

AbandonedBronco
10-23-2012, 03:28 PM
If you have the C, then you don't need to put any of the holes in the spacer. Just a big square opening like the intake has. However, some say that the individual holes do help with drivability, so might as well put them in if you can. Something about increasing air speed or the like.

The C series is a large, open intake that is designed for better flow at higher RPMs. It's what's recommended if you're wanting to build a motor for horsepower.

The DP series has the dual ports/planes in it. By design, it doesn't allow as much air through it (each runner has a divider in it), but the smaller passages increase velocity, which increases torque and gas mileage. It's more for mild to moderate builds.

That said, I have the C series on my '84 and the DP on my '81. Both have 600cfm carbs on them and I really can't tell the difference unless I really, really pay attention.

FordsForeverEric
10-23-2012, 03:31 PM
OK. I was just talking to my machinist teacher about it. He builds high horsepower drag engines, he said that it looks like its already set up for a 4 barrel. He acts like I don't need a spacer or adapter at all?

AbandonedBronco
10-23-2012, 03:50 PM
No, you don't need an adapter, a 4bbl will bolt right to your intake. The only time you'd need an adapter is if you want to use a 2bbl, or if you want to use a style of carburetor that has a different bolt pattern than your intake does. Different manufacturers use different bolt spacings, etc.

The reason for a spacer is to help with air flow. If the carb is too close to the intake floor, the turbulence right at the intake floor can impede the flow of air through the barrels. A spacer moves the carburetor away and helps alleviate this. Some people don't use one and say they can't tell any difference.

I also like to use one because I have a heated spacer, and I like the increased height of the carb when connecting throttle linkage.


A big word of caution about taking too much advice from your teacher. Drag strip engines and street engines are two completely different animals. Drag strip engines are meant to have the throttle fully opened with max power from start to finish. A street engine needs to operate at a multitude of different speeds, weather conditions, terrains, etc.

FordsForeverEric
10-23-2012, 06:45 PM
OK, It sounds like I still might want make a heated spacer. It never hurts to have a little extra room to work with :thumbup

I agree about the advice, I only asked him cause he's worked with engines a lot and knows what he's talking about.

After reading this thread more carefully and doing some reading on FTE... I still have some questions. I didn't realize that the port on the bottom of the intake connects to the exhaust manifold... Since mines EFI I'm planning on keeping the stock manifold, so do I just leave the bottom of the intake open?

AbandonedBronco
10-23-2012, 07:20 PM
Oh I agree, take what advice you can. :) Just be sure to keep things in perspective because it's a totally different area of expertise on engines. At least as far as builds go. Machine work and putting it together is all the same.

Mine has manifolds off of an EFI motor. They're great! The port on the bottom of the intake is fully closed so even if you don't do anything with it, it just sits there. But, as said, a lot build a plate that bolts to it that has an in and out port for coolant. Heating the intake floor makes a big difference. (Stock setup used exhaust heat).

FordsForeverEric
10-23-2012, 09:14 PM
Cool, sounds like i should make a plate for the bottom too :thumbup

And I got one more question for you... for now ;)

I noticed the that the flat plane that the carb bolts to is slanted towards the front of the engine, is there a mechanical purpose for this?

AbandonedBronco
10-24-2012, 10:49 AM
Yup. If you look at your engine closely, you'll see that the rear of the engine is lower than the front of the engine. The slant on the intake/carb plane is so that when the truck is level, the carb is level, even though the intake is bolted to a slanted engine.

FordsForeverEric
10-24-2012, 11:00 AM
That's what I thought, but I didn't have my engine in front of me at the time lol

Thanks again for all your 300 knowledge :beer

moncuremachinist
07-29-2013, 06:30 PM
I have a 1979 4.9L I installed a Holley 390CFM, Offenhauser Intake, and Hooker Headers. After the install, I had issues with keeping the engine running at less 1800 RPM. I suspect it is a vacuum leak at the intake/exhaust connection on the intake manifold causing it to run like it does. The Offenhauser intake did not appear to have any openings at this connection. Now that it is installed, it seems I may need a plate to blank off the plane where the connection was made. Without having to disassemble the installation, I was looking for some input on the problem. Has anyone else run into this issue?

AbandonedBronco
08-01-2013, 03:39 PM
How did the engine run before the 4bbl upgrade?
Was the intake new or used? If it's used, did you have it planed flat?
Are you sure you didn't crack a tab on the intake when you torqued it down?

Oddly enough, I've heard plenty of times that not being able to get the idle RPMs down is a vacuum leak issue, but I've had my fair share of vacuum leaks and never had a problem getting my engine to idle at the right RPM.

But, that's the tell-tale sign of a vacuum leak. Have you sprayed around the intake-to-head ports and around the base plate of the carb with carburetor cleaner? That's a great way to check for leaks. The engine will bog, rev, stumble, etc. when you spray cleaner on where the leak is.

As for the connection between the intake and exhaust. There is NO opening here. It is simply a cavity on the underside of the intake for heat. It's not open to vacuum or anything. If you're not using it, you don't need to do anything at all with it.

moncuremachinist
08-01-2013, 06:56 PM
Thanks for the reply AB. The engine/carb setup was stock before. The engine ran good before, just typical underpowered hence the upgrade.

The intake is new, as well as the gaskets, hardware, carb and header. All surfaces were flat and in good condition after visual inspection and with a straight edge.

I used propane instead of ether, as it should cause the engine rpms to increase. I sprayed propane around the entire manifold. The affected area was identified at the area of the heat riser, on the underside. It's hard to see under there even with a mirror. I inspected this area prior to the install and came to the same conclusion you mentioned, not open to the outside. I called offenhauser tech support and they confirmed what we both have concluded. There doesn't appear to be any broken tabs.

I am trying not to disassemble the setup to troubleshoot the issue, but that may be the ultimate course of action. I am curious what other things I should check.

AbandonedBronco
08-01-2013, 07:05 PM
Which style gasket did you use when you put it back together? I haven't had the best of luck with the stock Felpro replacement gasket. The Mr. Gasket #260 is a much better sealing setup.

Other things in that area are the base plate, and throttle shafts on the carb (if there was by chance a manufacturing defect).

What did you use to bolt it back on? Did you use the stock bolts? Or something aftermarket?
Headers are often thinner than the intakes, so they require a "stepped" washer or surface when bolting it down. If not, the washer will be at an angle and won't properly seal. Sometimes, people will grind one side of each washer down to fix this. I've also seen header fastener kits sold on places like Summit.