backfiring through exhaust

grumpuscreature said
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.

Thats what I would think too, but if ot has a .480 lift cam, I would almost wager that the timing chain is a double roller or double setup with steel gears. On a stock small block, the nylon gears sometimes wear down or come off, causing the timing chain to skip a tooth. The weak link type chain can also stretch on top of that. However, in this case, witht the aggressive cam, I would say that it has a better timing setup and is probably not the case. I know the comp XE line of cams, like my 268, like around 14-16 degrees of initial timing. 11 degrees initial gave me a slight backfire through the carb, but when I gave it 15 or so, it went away and runs great.

Check into what your cam likes best, especially with that carb cfm. What is your engine size and cam manufacturer?

Could be a slightly worn cam lobe, but I would expect coughing at all rpms and a rough idle, so I doubt it.

Look into the carb a bit more and make sure your cam has its sweet spot of timing.

Good luck and we are here to help. Happy New Years to all!!!!!:toothy10: