I have a holley 800 came off a basicly stock 454. My buddy asked me to look at a co workers new mild 454 carb that his engine builder told him this carb was no good. I went through it seemed great cme back with it and he bought a new carb, same popping problem. I went over and seen started with the basics.....and yes the firing order was wrong. Anyway you can pm me if interested, its a great carb with no corrosion. Not to big Imo. Good luck. Darren Oh, model #4780 double pumper