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Old 11-29-2012, 02:10 PM   #1
speedyweasel
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Exclamation Daily Driver Down

Started up the engine leaving the gas station the night before last and heard a disconcerting pop (maybe a large backfire?) that seemed to come from the top end of the engine. Noticed no issue at low speed but it was abnormally weak as I approached 30 mph. Driving around yesterday it wouldn't go over 35 without massive hesitation, though no mechanical noises other than just the bogged down engine. Inspected vacuum lines thinking maybe a backfire might pop off a vacuum line. All vacuum lines seem to be where I last put them. And it runs and revs fine with no load on it.

Pushed the engine a bit last night to see what it would do... oops. Heard a sickening thud -- but it kept on running and there were no follow up sounds and the running condition didn't change. Runs ok at low RPM.

I've never had the valve covers off before and THINK I've been hearing a ticking from the passenger side head so I pulled off the valve cover. Nothing abnormal except the intake rocker & pushrod on the farthest cylinder have a pretty thorough layer of rust on the top -- but only on the top. Everything from there down is smooth, clean and shiny. All pushrods are straight. All rocker arms were tight. All springs are intact and seated. No valve stems LOOK bent.

Other than yanking the driver side apart, too, I'm at a loss. I can toss it back together but have to figure out why I have no more power after that backfire at the gas station...

















What am I missing here? What should I be checking?
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Old 11-29-2012, 02:28 PM   #2
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Is that water beaded up everywhere? What carb are you running? If it backfired, you could have done damage inside the carb. Do you have a spare? If it runs fine at idle, but under load it bogs, you have leak somewhere. Spray some carb cleaner on the carb and if the idle comes up, then start paying attention to the carb.

I say all this, because your description does not include any knocking, etc that is persistent. Even if you dropped a cylinder, it would still run better than described. Heck, I once started my BKO with all 4 plug wires disconnected on the driver side and it ran at idle!
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Old 11-29-2012, 02:35 PM   #3
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The water is new... it's raining here. I've been trying to keep it out but some got in anyway. There was no sign of water in there til I cracked it open.

The carb is a Carter AFB Competition Series... basically the Edelbrock Performer. I have to put it all back together to try the spray idea (which is a good one - wish I'd thought of that before tearing into it).

No spare carbs.
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Old 11-29-2012, 03:11 PM   #4
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You say it's been raining, how are your distributor and plugs? My 400 and carter comp did this to me a few times. Subscribed and interested in what you find.
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Old 11-29-2012, 03:21 PM   #5
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Rain started after the problem (by about 36 hrs). About to pull the plugs. Dizzy looks alright but I could stand to replace the cap & rotor.
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Old 11-29-2012, 07:16 PM   #6
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IFthe engine has high miles, I would suspect a jumped timing chain.
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Old 11-29-2012, 07:54 PM   #7
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A backfire could've been the "power valve" inside the Carb at the metering block took a dumpthey just scew into the block, easily replaced NBD......how does it run right now when you start it up.....?

You can pull off the bowl, gasket and replace it to see if that might help.....IDK - just a thought and clean up that rocker arm and pushrod or replace them ....can't be good for peerformance you know...


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Old 11-29-2012, 09:28 PM   #8
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Carter's have power valves?I'm wondering what the backfire could have damaged to make it run like that...I'm stumped as well.when was the last time you messed withe Carb?

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Old 11-29-2012, 09:32 PM   #9
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I'd do a compression test, and check all the plugs while they're out. A lot can be determined by these 2 simple checks. Also, check ign timing.
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Old 11-29-2012, 10:11 PM   #10
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Quote:
Originally Posted by speedyweasel View Post
Started up the engine leaving the gas station the night before last and heard a disconcerting pop (maybe a large backfire?) that seemed to come from the top end of the engine.
What am I missing here? What should I be checking?
Could it be bad gas? You just filled up. Was it a gas station you normally use?
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Old 11-29-2012, 10:54 PM   #11
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Quote:
Originally Posted by 7LBRONCO View Post
IFthe engine has high miles, I would suspect a jumped timing chain.
:eek

X25,xxx miles. Supposedly 125,xxx but who knows?

Quote:
Originally Posted by JKossarides View Post
A backfire could've been the "power valve" inside the Carb at the metering block took a dumpthey just scew into the block, easily replaced NBD......how does it run right now when you start it up.....?

You can pull off the bowl, gasket and replace it to see if that might help.....IDK - just a thought and clean up that rocker arm and pushrod or replace them ....can't be good for peerformance you know...
Carb was recently done by a friend who used to run a carb rebuild shop. Not to say he didn't make a mistake but I think he probably did a good job. Since it was rebuilt maybe 1,000 miles ago, it ought to be fine I think. It has "popped" since I first got it, though, so maybe it needs different jets...?

Quote:
Originally Posted by Robs79BBbronco View Post
Carter's have power valves?I'm wondering what the backfire could have damaged to make it run like that...I'm stumped as well.when was the last time you messed withe Carb?
See above

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I'd do a compression test, and check all the plugs while they're out. A lot can be determined by these 2 simple checks. Also, check ign timing.
I asked a couple of locals if I could mooch a compression tester and the only one who has one is out of town til this weekend. :doh0715 The plugs I bought are spec'd at the right gap for the stock tune. (One good reason to buy Motorcraft.). Stock gap was .045". Wasn't able to do a compression test while the plugs were out but I still intend to run one this weekend.

Quote:
Originally Posted by BakerBaker View Post
Could it be bad gas? You just filled up. Was it a gas station you normally use?
Fair question, but I've bought there numerous times, including for the '04 Excursion which I would suspect to be less tolerant of crap fuel.

UPDATE!!

Reinstalled all rocker arms and push rods after cleaning up the rusty one. Cleaned up the nasty old valve cover and hit it with some paint. Replaced the spark plugs with new Motorcraft platinum deals. Decided to inspect the carb like you guys suggested and -- sure enough -- the blowback closed the choke part way. It's a good stiff choke, too. At any rate, that was the cause of the odd lack of power under load. It was getting enough air at idle and modest throttle, but once it needed a lot of airflow, it couldn't get it with that choke closed half way. The thud remains unidentified but I drove it ten miles tonight without incident.

Anybody know if California will pass you on a smog check if you have a crankcase breather on the passenger side instead of that thing returning the gases to the air cleaner?

Cleaned for reinstallation.






Churched up the stock valve cover a bit to match the air cleaner.










Thanks for the help, guys!
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Old 11-30-2012, 12:14 AM   #12
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Speedy, I have a compression tester you can borrow if you still want to run a check on your engine. If Carter's do have a Power Valve and you blew it out when your engine backfired, this would cause your hesitation and lose of power because the engine is running rich.
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Old 11-30-2012, 12:54 AM   #13
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Been there done that with the PV problem Charlie and I'v done the choke thing also back in high school. Glad to see you figured it out.
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Old 11-30-2012, 08:36 AM   #14
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so where was the moisture coming for it to rust up the push rod or is that from it sitting for a while before you got it.
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Old 11-30-2012, 09:51 AM   #15
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Is the valve cover breather collecting moisture and letting it drip down on your rocker and push rod?
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Old 11-30-2012, 11:40 AM   #16
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Got a compression tester and spare rockers and pushrods if you need them.
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Old 11-30-2012, 12:47 PM   #17
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Quote:
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Is the valve cover breather collecting moisture and letting it drip down on your rocker and push rod?
I was thinking that, myself. It's the only cause I can come up with.
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Old 11-30-2012, 01:52 PM   #18
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Quote:
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Speedy, I have a compression tester you can borrow if you still want to run a check on your engine. If Carter's do have a Power Valve and you blew it out when your engine backfired, this would cause your hesitation and lose of power because the engine is running rich.
Thanks, Ziggy! I think I'll take you up on that. Give you a call to see when you'll be around. Thanks.

Quote:
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Been there done that with the PV problem Charlie and I'v done the choke thing also back in high school. Glad to see you figured it out.
The choke hasn't been necessary since I got the fuel mixture set up a bit better. Thinking I may just remove it. Hmm...

Quote:
Originally Posted by thin blue line View Post
so where was the moisture coming for it to rust up the push rod or is that from it sitting for a while before you got it.
Quote:
Originally Posted by cheepsk8 View Post
Is the valve cover breather collecting moisture and letting it drip down on your rocker and push rod?
Quote:
Originally Posted by American Thunder View Post
I was thinking that, myself. It's the only cause I can come up with.
Sh1tty gasket seal from the little emissions hose that's supposed to connect to the factory air cleaner. It was so rigid and cracked so thoroughly that I decided to remove it and stuffed a rag into it until I can head back to Vatozone to grab a little PCV air cleaner thing. I don't use the stock air cleaner anymore anyway so the hose has been just hanging there unfiltered and open. I have a Summit Racing cleaner on it now. Maybe I'll look around online first. Time to hit the "Post a Pic of Your Engine" thread for some ideas & PM the guys who have one that looks good.

Quote:
Originally Posted by Cymon Sez View Post
Got a compression tester and spare rockers and pushrods if you need them.
Thank you. The rocker arm and pushrod are covered -- took a VERY light sanding on the rocker arm and a moderate sanding on the push rod to clean them up. Once I mooch Ziggy's compression tester I should be alright.

I drove it to the train station this morning with no issue at all. It still pops a bit when I quickly let off the throttle at speed (as opposed to easing off the throttle) but it accelerates and cruises with minimal issues. There's a "dead spot" in the middle there between easy throttle and WOT that seems to lag but I've had that since I last farted around with the fuel mixture. I'm learning as I go with this thing. I called around earlier this year to find a shop with a decent reputation to tune it for me. All the low-rent shops said they could "give it a shot" (yeah, that inspires confidence) and the good ones all said the same thing -- take it to Riverside Carburetor and Electric. So I called them for some idea as to how much they'd want. Apparently, they're quite fond of their work. $600.00 to tune the carburetor and a 1-week lead time. No thanks. That's over 1/4 of what I have in the entire truck so far. It's a hot rod shop with a stellar reputation but that's just ridiculous.

At any rate -- it's running reasonably well. I'd like to figure out the "flat spot" and the popping but it runs pretty well for now. Once I do the compression test, I'll post up but probably on my build thread so I can find those values later for reference. I haven't been as detail-freak oriented as "Bronco" John Galt but it helps me keep track of some things.
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Old 11-30-2012, 01:55 PM   #19
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Is the valve cover breather collecting moisture and letting it drip down on your rocker and push rod?
Oh, and it spent about 2 yrs as a lawn ornament in Big Bear, CA before I picked it up. At some point, it was a ranger's vehicle for a kids camp in the mountains somewhere, too. So I know it spent some time sitting around in higher elevations & colder temps. Beyond that, I'm not sure. The valve covers have been off at some point because the gasket I removed was a Fel-Pro cork like the one I reinstalled.
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Old 11-30-2012, 03:14 PM   #20
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What year is your BKO ....?

There's no guarantee that new parts out of the box can't be faulty or take a dump.....BUT I'd also take a look at your PCV = positive crankcase ventilation valve and see what conditon it's in otherwise replace it with....http://www.oreillyauto.com/site/c/de...2180&ppt=C0023


Good Luck ~
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