engine is popping through the exhaust.

[atvrider85]

I have a 86 K10 that has a 97 vortec 350 with a carb installed on it. Engine has around 50,000 miles on it. Last couple of weeks intermittently when the truck is at idle or at idle with the transmission in gear it will have a popping noise coming out of both exhaust pipes. I have changed plugs but i didn't change the wires, they are taylor 8mm wires. Vacuum gauge is pretty much steady with very little needle shake at 18 mmHg with the air fuel needles on the carb adjusted properly. Intial ignition timing is set at 10 btdc. The exhaust is long tube headers with 3 ft of pipe then a 40 series flowmaster. No major leaks in the exhaust. The engine runs great and i am having trouble track down the issue. Any thing i could be missing. Thanks for the help.

 

[rich weyand]

Which vacuum advance canister is on it? You should be able to see the stamping on the tang of the advance mech between the canister and the distributor cap if you look straight down into that gap.

 

[atvrider85]

The distributor is a aftermarket MSD streetfire distributor.

 

[rich weyand]

The distributor is a aftermarket MSD streetfire distributor.

Not what I asked. What is stamped on the vac advance can?

 

[rich weyand]

Per these instructions, what did you set the vacuum advance limit at?
http://www.msdignition.com/instructions/Products/84281.pdf?terms=84281

 

[85c10owner]

No major leaks in the exhaust.

Any exhaust leaks can cause this. Replace the gaskets at the head and the collector and see if that fixes it.

If this just happened out of the blue I dont suspect anything with the timing. If this started happening after messing with the timing then that could be your problem.