backfiring through exhaust

moparguy said

My plugs are new. Have 750 cfm holley, runs a little rich, stock ignition components, but also new. Other than my coil, have 12 degrees of intitial timing. Plugs don't look fouled. Is it normal for my timing light to miss the mark every now and then? That is why a suspect something on the ignition side.

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What is your engine size? 318's like 7 degrees initial and 360's 9 or 10. IMO 12 is a bit much. It is normal for the timing light to miss the mark every now and then if the timing chain has stretched. Sounds to me like your chain has stretched and you're running the cam retarded. Put a timing light on the beast and have a long, careful, look at the timing marks. If the mark seems to be moving at all or skips entirely from time to time and wavers a bit before settling down, change the timing chain. They are the Achilles heel of smallblocks.