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Re: C2, 396/425, back firing, coil?
Most likely the problem is with material in your carb., dirty fuel lines, clogged fuel filter, rust in your gas tank. -
Re: C2, 396/425, back firing, coil?
Dave:
Does your engine backfire out the intake or the exhaust?
If it's popping out of the carburetor, the first thing I would check would be the cap and rotor. Look for carbon tracking between the posts on the cap and look for burning in the center of the rotor where the spark could jump to the distributor shaft. You could even have knocked a lobe off the cam on the exhaust side.
If it's backfiring out the exhaust, I might suspect a flooding carburetor which would also explain the strong smell of gas.
This is assuming the car started and ran correctly for awhile and then progressively got worse.
MikeComment
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Re: C2, 396/425, back firing, coil?
If it ran fine for a while, and then something changed, and if it is backfiring out the carb, then the timing "changed" for some reason. It could be something with the cap or rotor, but those usually degrade performance slowly - not dramatically in a single event. The "single event" that happened to me once, was that a loose, sloppy timing chain jumped a tooth or two, changing the timing and causing backfiring. Also, check to see if the dist is loose and could have moved. Try to get it running enough to check the current timing with a light.Comment
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Re: C2, 396/425, back firing, coil?
If the exhaust smells real rich, mayby some smoke from the exhaust I would suspect a power valve failure. This is the first thing I would check. A failed power valve is a pretty common failure with Holley's during my almost 30 years of having them on my 68 and 70.This is a easy part to replace anyway. I have found parts for my Holley's at Auto Zone. They sell fuel bowl gaskets, metering block gaskets, and power valves in individual packages. Just because you have it apart, a new accelerator pump replacement might be in order.
No one has given me any feed back on this, but this has worked for me. After starting the car remove the air cleaner lid and put you finger over the front veritcal vent tube. If the car dies right away I always replaced the power valve and it was fixed. My Holley's will run a lot longer with a good power valve if a finger is used to close off the same vent tube.Comment
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Re: C2, 396/425, back firing, coil?
It is poping through the exhaust, I will replace the carb tonight. It is not the original carb. and I just want to get the car running.Comment
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the finger over
the vent works because if the PV is leaking you are putting pressure in the float bowl and it will force excess fuel directly into the manifold thru the PV vacuum hole in the carb base. if the PV is good the pressure will push fuel out of the booster nozzles and this will take a few seconds for the fuel level to raise enought to come out the booster.Comment
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Re: C2, 396/425, back firing, coil?
10-4 on the finger. I heard this a long time ago. I used to run Holley's on everything. I guess I had the mis-fortune of never having a backfire and blowing a power valve. But, I still have a Holley on one of them, regardless of what anybody thinks of them.Comment
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