I have a 468 BBC drag car with BG KD carb. I just replaced restrictive mufflers (very quite) with race mufflers. Immediately the car would not idle. Made slight increase in idle adj and car seemed to idle OK. Went to track and car backfired through the exhaust througout the run. Fuel pressure has always been high at 10 psi. Should changing just mufflers caused this. BG and Holley both say I'm running out of fuel (Holley Blue pump can't support 650 HP). Previous owner had pressure high to compensate fuel supply. Does all this make since to cause popping in the exhaust? Old school would say popping in carb is tuning, popping in exhaust is ignition. I'm confused.