Holley 750 Questions

exactly buy a renew kit and rebuild it that holley you have probably has some dryied out gaskets and accelerator pump diaphram.  
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Hi guys the Q-Jet works great. After 3 oil changes and new plug wires I finally got it to run good. I put a new power valve in the Holley and reinstalled it still has the rich condition at idle. I think over winter I will get a Holley trick kit and rebuild it. Thanks to every one that gave me some ideas to help me out. This is a great forum and a lot of great guys.  

Have you tried running a hotter plug? If not try the ac delco R 43. My 780 was running very rich on my 70 gto . I have a 455. My carb is basicly new , I replaced the sec. diaphram due to ahole in it and put a lighter sec. spring in it and leaned it out a little. It runs very strong, but doesn't have that "gawumpp" and then all hell breaking loose like i have had with other cars that weren't built like this one. So I am going to try a 750 or 850 with mech. sec. My initial timing is 18deg. and my advance is at 36deg.It doesnt bog it is just a smooth hard pull. My plugs no longer rich looking; they are nice and tan.I have always heard to get the timing correct ,then address the carb issues. I still don't understand where my gawuump is. It has to be in those vac. sec. My chevelle ss had mech. sec. and when you nailed it all hell broke loose at once. The same thing with my camaro ss (70) with an lt 1 with angle plug heads. Holley says the 780 vac. sec. is one of the best street strip carbs available.Does anyone have an opinion on my carb dilemma. I think it needs a 750 or 850 dbl. pmpr. w/ mech. sec. It's a 455 bored.030 w xe 272 comp cam, rpm air gap and # 16 heads with an m-21 4sp. and 4:10 gears. Any help would be greatly appreciated. Thanks ,Dave  

Hi thanks for the reply. I did replace the power valve with a new one it didn't help.  

Have you checked all of your' manifold bolts and made sure they were tight? I did all kinds of things to find out why my GTO wasn't running quite right. I had finger loose intake bolts and my carb bolts were loose also. I found my vac sec. diaphram had a hole in it and I also put in a much lighter sec. spring as well as ac delco 43 plugs which are much hotter. I really can't say what made it hit harder. I also run initial timing at about 18 and my advance is 36 at 2500 rpm. It runs real strong, but i have never had a vac sec(780cfm, it's new)before and it doesn't have the hit that my other cars had that had mech. sec.This car is aframe off resto done in 07 and has about 2300 miles on it. It's got a fuel cell, nitrous( which I have never run)455 bored .030 w/ keith black 10:0 -1 pistons, xe 272 comp cam,edelbrock rpm air gap intake, supposedly #16 heads. I will find that out tomorrow. It also has an oil cooler ,line lock,and an msd6-al ignition and pro billet distrbutor. Damn, those are some excellent quality parts. I still think my old 70 camaro ss w/lt-1 in it ran stronger.I'm baffled about that. Good luck and check this simple stuff first, unlike me. Dave