I have a 73 C20 454 that I rebuilt the engine, rebuilt the heads (spings, valves, etc ) It has an Edelbrock gear drive,Performer cam, and 750 manual choke carb. I rebuilt the distributor (Accel super coil, etc, etc). It does'nt backfire all the time. (just when I'm trying to show off) Sometimes I mash the loud pedal and it slams you . next time it backfires out the carb farts and sputters then takes off like abat outta hell . trashing the air cleaner in the prosess. I want to put this in my K5 blazer . but not acting like this . Any thoughts would be apprecieted .