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Joined: Mar 2003
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On my '67 Chevy 230" I've got a 390 Holley (8007)carb on an Offy intake with the Stovebolt cast exhaust manifolds. The head was recently redone, and compression is real good, but I can't get it to idle or run smoothly once it warms up. The back 3 cylinders seem to be where the problem may be according to sound of the split pipes. The plugs don't look bad. Any thoughts, ideas, suggestions are greatly appreciated!
Thanks, Brian F. #3480
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Joined: Jun 2002
Posts: 315
Contributor
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Posts: 315 |
Check for a manifold leak. I had a similar problem this spring. I re-gasketed the intake (Offy) and headers (Clif) and also remounted the carb.
I/I #4101
'71 GMC Jimmy 350, sm465, np205,3.73 posi.
'68 C/10 Stepside 292 (.030 over) Offy Intake, 500 CFM AFB,Clif headers, sm465, 3.73 posi.
'67 K/10 454 project.
'72 K/5 rolling frame project.
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Joined: Mar 2004
Posts: 757
Major Contributor
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Major Contributor
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Brian,
I don't remember when I saw your car if the carb is mounted front to back or side to side. There has been a lot of opinions on why or why not to mount 4 barrels sideways on those engines.
If you remember my 250 I am running the Offy with an Edelbrock 500 on it sideways and I've had zero problems.
If you can't get the problem resolved after checking for the usual vacuum leaks, etc give me a call and we can kick it around over the phone or I will even take a ride down and we might be able to solve it together.
Mike G ( 4355 )
Mike G #4355
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Joined: Jul 2000
Posts: 4,622 Likes: 25
1000 Post Club
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1000 Post Club
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Posts: 4,622 Likes: 25 |
If you seem to only be having problem to the Last 3 cyl. Have you thought about also rechecking Valve lash??? A carb in it self would not show Problems to only 3 chambers No matter what way it sat on the intake. If it is in the Last two I would say Yes a Intake issue But with it seemingly to be ??sounding?? as the Last 3 chambers ?? Problem I see with that Is it would also have to effect the 3&4 Now 4 ,5 6 Because if 4 had a Intake issue So should Number 3 Knowning That 3&4 are on the same runner. I would say Pull each Plug wire to see if the Motor changes any. One Other trick You can do Which Hurts Nothing Is to Take a squirt Bottle to all the Header tubes and see How the water evaporates off Each tube This will help pin point a chamber/cyl. issue??
#3220 }[oooooo]
Larry/Twisted6 [oooooo]  Adding CFM adds boost  God doesn't like ugly.
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Joined: Mar 2003
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Thenks to those who replied...it appears to have been the power valve. It's the weakest link in a 390 Holley, as all it takes is one pop back thru the carb to destroy it. Supposedly there's a kit to eliminate this problem, which I ordered and we'll see if it works.
Thanks again, Brian.
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