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I just bought an '80 Bronco for $600. It needs front brakes and it runs a little rough. I got the brakes taken care of, now I need to figure out why its not running well. According to the previous owner, it has a '78 351W with a Holley 4 bbl carb. It was supposedly rebuilt 38k miles ago.

First thing I noticed was that the coil was arcing. So I replaced the cap/rotor, spark plug wires, and plugs. Next thing I noticed was that there was a vacuum hose on the carb that was capped, but loose. I put a hose clamp on it and the motor ran a lot better.

Its still running a little rough though. When cold it runs very poorly. It hesitates and almost stalls. This happens when I give it gas. If I roll into the gas slowly, it will accelerate fine. Once I'm rolling, it runs fine. When its heated up, the hesitation starts to go away, but never completely.

Any tips on what I should look for would be greatly appreciated. I'm at work right now so I can't post any pics until tonight. I'm not too familiar with carbs so its a little frustrating. I don't want to go in there turning screws and messing it up.
 

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Sounds like a problem with the choke. And let it warm up before driving it, most carb'ed engines don't like to be driven cold. Best thing for you to do is, get a Haynes repair manual
 

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It hesitates and almost stalls. This happens when I give it gas. If I roll into the gas slowly, it will accelerate fine. Once I'm rolling, it runs fine. When its heated up, the hesitation starts to go away, but never completely.
Sounds like a lean stumble off idle. Try larger shooters, and experiment with the acelerator cams.

After you get rid of that bog off idle you can go after the jets to fine tune it.

What Holley is it?

And yeah make sure your choke is working properly.
 

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HOLLEYS ARE REAL COLD NATURED. I HAD ONE ONE MY 82 TRIED EVERYTHNG TO GET IT TO RUN RIGHT. FLOODED AND STUMBLED REAL BAD WHEN OFFROAD. EVEN BOUGHT A NEW ONE STILL DID THE SAME THING. TRY A ELDERBROCK 600CFM WITH ELECTRIC CHOKE. YOU CAN GET A REMAN ONE CHEAP FROM NORTHERN AUTO PARTS. THEYRE WEB SITE IS WWW.NORTHERNAUTOPARTS.COM PART#9906 $209.99 I PUT ONE ON MINE NEVER TURNED A SCREW RUNS GREAT!! :)
 

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Discussion Starter #7
Thanks for the ideas so far guys. I'll post some pics tonight. I'm not sure which Holley it is. All I know is its a 4 bbl, looks to have an electric choke. I believe the guy that installed it did a hack job. There are capped hoses and stuff all over the place.

Did these motors have any emissions equipment (egr, pcv, smog pump, etc?) Looks like all that stuff is missing, if it ever was there to begin with.
 

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on that piece that surrounds the choke butterflies there should be some numbers. write them down go to the holley website and match them up to there spec sheet. it will tell u every little detail about the carb u have. or post the numbers, i have a holley book that has all the numbers in the back
 

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Sounds like a timing problem, check it, advance it a few degrees.
any idea what comp ratio that 78 windsor is??

Also, your fuel filter could be clogged( looks like it.... a metal Fram will do the trick), your carb could need a can of carb cleaner ran threw it (valvoline makes IMO the best carb cleaner).. actually it does by looking at those pics. For 600 bucks you definatly didnt do wrong for that thing!!

Was gonna post a pic so you could see my filter set up, but Superford lost a whole bunch of mine apparently and this one doesnt show it. but did all the work to look for it so figured id post one for people to drool over (JK:twak)

 

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Discussion Starter #12
81Bronk36 said:
Sounds like a timing problem, check it, advance it a few degrees.
any idea what comp ratio that 78 windsor is??

Also, your fuel filter could be clogged( looks like it.... a metal Fram will do the trick), your carb could need a can of carb cleaner ran threw it (valvoline makes IMO the best carb cleaner).. actually it does by looking at those pics. For 600 bucks you definatly didnt do wrong for that thing!!

Was gonna post a pic so you could see my filter set up, but Superford lost a whole bunch of mine apparently and this one doesnt show it. but did all the work to look for it so figured id post one for people to drool over (JK:twak)

81Bronk36, thanks for the tips! If you email the pic to [email protected] I will host it for you.

Is the only fuel filter the inline filter in the pic? I'm used to having a big fuel filter back near the fuel tank.
 

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any time I install an aftermarket carb (oh about 8 times in 2 years) I put an inline filter in. Its 1.) added protection 2.) easier to change 3.) easier to install I stay away from plastic ones cuz they give a little around the clamp and let air in. Other then there PCV and fuel filters... Fram sucks!
 

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Discussion Starter #14
Well, I cleaned out the carb real good with carb cleaner. It made a huge difference! Its almost at 100% smooth operation. I will replace the fuel filter this weekend and hopefully solve the hesistation problem completely.

I'm also taking it to a local Mustang shop I work with to check the timing. I suspect its set pretty conservatively. I don't know how snappy these motors are supposed to be but my feels like its on the sluggish side. I would expect a lot of low end tq out of the 351, especially compared to the 281 in my Mustang (apples to oranges though, I know).

Btw, I checked the Holley website. My carb is the 4160 model. 600 cfm.

Thanks again guys. This is an awesome site!
 

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Cool im glad you got it cleaned out!

Why not spend 60 bucks on a light and check the timing yourself though???

Just wondering??
 
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