i have a 82 chevy k10 with a 400sb when i start it up and let it warm up for a while sometimes as long as 25 to 30 mins. and i rev it up it backfires thru the intake. i put a new carb on it holley street avenger 770cfm and it has new fuel pump. the exhaust leaks a little on bank 2 in between the header and block. i have also put the timing light on it and its right where its suppose to be. this truck has been sitting for a long time before i got it