ok ive got an 81 with a 400 small block and when i put the pedal to the floor and then let off it backfires really nasty it sounds like a gunshot from my engine lol. what could this be due to im really new to carb engines and to this truck i just bought it, my thoughts are too much timeing or bad carb. please help me out and if you need more info on the engine ill supply as much as i know.also does it affect the performance having this problem? as far as i can tell this truck hauls butt and doesnt hesitate so other than the embarrasing backfire i dont see a problem.