I had a Holley 650 with a 4.5 power valve and the car ran great. I decided to try a new 750, so I put the 4.5 powervalve in this carb and the car won't even run. I have to have the idle turned way up so it will idle. About an 1/8 inch of the transfer slot showing underneath the butterflys and the idle mixture screws has absolutley no affect when I turn them in or out. I know the car should want to die when they are turned all the way in. My floats are fine. The only thing I can think of , but I am not sure, is the jetting is way to high 71 in front, 80 out back. It wants to pop through the carb and backfire like a lean condition though. I put all new gaskets and new 4.5 powervalve. The 650 has 67 and 73 jets in it. If a carb was really rich would it still pop and backfire out the carb. I need help. Thanks, Erik Beckett
68 Camaro RS, Built 355, 274 Comp Cam, Sportsman II Heads 200 c.c. 2.02. Ported to Performer RPM Manifold and 1.75" Headers, 1.5 Roller Rockers, 650 Holley, Steel Crank, 4.11 Gears but no posi yet! TH350 tranny w/ shift kit.