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Old 12-17-2004, 07:04 PM
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Backfire at idle

Hello folks, while at idle my 350 backfires or pops out of the driverside only. I did a search on the site and someone suggested for a simular post that it was possible to have two wires crossed. I checked them and they are right, so what is the problem. It starts fine and idles fine except for the poping. Is it possible that I may have a stuck valve? Thank you for any help!

350
mild cam (not sure of specs)
hei w/the adjusted weights and springs (middle range)
accell super coil
headers
holley 600

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Old 12-17-2004, 07:05 PM
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Exhaust? Could be a valve train/bad lifter problem.
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Old 12-17-2004, 07:10 PM
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Yes, the exhaust. How can I track it down? Cylinder pressure test?
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Old 12-17-2004, 07:12 PM
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Yes, then after you find the bad cylinder pull the valve cover.

it is also possible that there is a bad plug or wire. does it miss when you rev it up?
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Old 12-17-2004, 07:15 PM
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Have not noticed it while driving, but it does when I let off the gas and coast.
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Old 12-17-2004, 07:43 PM
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Driving is ok. Idle it pops out the exhaust. on decell it pops. correct?

does it have an exhaust leak?

is your carb tuned?

are your plugs and wires good?
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Old 12-17-2004, 07:52 PM
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Correct at idle and deceleration
Plugs are new
wires seem to be in good shape, no obvious damage
have not put the vacuum on the carb to tune yet, tomorrow
maybe a small exhaust leak around header collector

One other thing-a friend told me to pour Marvel mystery oil down the carb, if it was a stuck valve it may free it up. I don't think I like that idea. Anyone ever did that before?
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Old 12-17-2004, 08:00 PM
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leaky collector, eh? that can cause popping on decell

Pull the plugs and see that they are all brown. run the compression test and see how the cylinders compare.

also do you have vacuum advance hooked up? if so port or manifold? port or no vac advance can cause popping on decell also.

at idle is almost something in the valve train

Last edited by NXS; 12-17-2004 at 09:17 PM.
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Old 12-18-2004, 07:44 AM
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I do have the vacuum advance hooked up to the port (base of carb). I am going to pull the plug and isolate the cylinder, then pull the valve cover an take a look at it. If the valve is stuck, I should be able to tell with the cover removed, right?
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