Bad Cam, or?
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From: Wyoming
Bad Cam, or?
Hey guys, My old pickup developed a problem and I cant quite figure out what it is. Its a small block 351, edelbrock carb, pretty fresh heads. It runs and starts fine, but when you start rapping it up and the secondarys begin to open it starts popping out the carb, no popping till you rev it up though. I keep hearing different things, mostly a flat spot on the cam, but then someone said it would do it all the time if that was the case. So any help would be appreciated before I go tearing into it.
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Joined: Jul 2002
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From: Bend,OR
sounds like either a vacum leak or a fuel deliver issue. i am no carb man by any means though. whats the timing set at? and when was it tuned up last. have you checked the spark plug wires for crack and make sure they are all secure on the plugs
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TWhen you say loads up, do you see puffs of black smoke? If you do, I would go with Kemicalburns on the ignition and timing issue...........if you don't see black smoke, I would check for a fuel delivery problem. Maybe a way low setting in the secondary float or a fuel pressure issue. Temporarily hook up a fuel pressure gauge and see what you have when you gas it. Popping in the intake is usually caused by a lean out. The fact that it runs good on the primaries, kinda rules out the vacuum leak and the flat cam, but then you never know. I've been fooled before.
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Joined: Nov 2004
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From: Tucson, AZ
along the lines of the vacuum leak, could be the dist is not advancing properly, which i have seen cause popping problems. is your dist controlled by engine vacuum? what condition is the carb in? cheers, garsten
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From: Wyoming
I havnt really noticed any black smoke, I have another good edelbrock carb Im going to try and throw on tonight. I was wondering about the distributor not advancing right, Its the original distributor with well over 300,000 miles on her. It might be time for a new one, lol. Thanks for the help though guys, Glad to hear it probly isnt a cam. Ill get back to ya tonight to see if the carb solves the problem.
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Joined: Feb 2006
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From: Wyoming
didnt get to swapping carbs tonight. checked fireing order, wires and any possible vacumn leaks. Anyways, I think the motor has around 80,000 miles, which would include the timing chain, the heads probly only have like 40,000 miles on them. The truck has over 300,000 and im pretty sure its always had the same distributor. Also, tonight, My local engine builder pretty much told me its the cam for sure 
Or possibly a broken valve spring. He told me to pull the valve covers and watch the rockers, I wish this was an easier diagnosis
Or possibly a broken valve spring. He told me to pull the valve covers and watch the rockers, I wish this was an easier diagnosis
