My question is when does it pop in the exh ? If it does it on decell then check the header gaskets as if they leak a little it can suck in air and the mixture is richer on decell since the throttle is slammed shut basically and it still has fuel going in but the air is cut off and if it pulls air in the exh system from a small leak it will pop in the exh. Kinda like what and air pump will do if the diverter valve goes bad. But thats if it pops on decell. Ron