I have a factory 71 Big Block Chevelle. The engine is correct 71 block, 73 454 heads, Edelbrock Hi-rise intake, Holley 670 Avenger, HEI, Headers. This issue is that normal running and low speed driving is fine. If you try to pass or speed up to get on the highway, the engine spits and sputters and fails on its face. Engine timing is set at intial 16, 44 ac spark plugs. Any help would be greatly appreciated. If the above is not enough information let me know.

have you checked your floats? i had the same prob with my 750 holley. out of the box floats were way off! causing it to flood out and shoot fuel out the primary fuel bowl at higher rpms. this was with stock fuel pump with 7psi at most. is that what you mean by the engine spitting?(fuel)

Thanks for the reply. Yes, that is what I meant. It also sounds like it is backfiring through the carb - but, just slightly. I replaced the power valve - did not help. Has anyone ever had trouble with a carb being to high? I have a hi-rise intake and a 1 inch spacer. The spacer was necessary because of a base vacuum port on the carb would not seal properly against the intake. It does seal now, but I still have a problem.

i had to put a rgulator on my 750 (5and a half psi) to stop that crap! i tried every thing else first.....power valve.....shooters........jets........timing...... .idle mixture 10 times..... some how i just had too much pressure.......holley techs said 5and a half psi is plenty and i havnt ran my bowls dry yet? so i guess im cool for now . not sure about your height? is a 670 enough? i used the carb calculator on this sight and my 468 needs 744cfm.

I'm thinking you have a couple issues. Try to fix one at a time and judge performance change as you go.

First - timing. Sounds like it probably needs to be advanced more.

Second - MAYBE the carb is a little small. Maybe. Sounds like you are running on the lean side during transition to the secondaries and when you first step on it. Probably has an off-idle stumble too I'll bet. If the timing change doesn't fix the stumbling, try a larger shooter size.

Third - vacuum secondaries? If so, it's possible they are opening too soon. Again - do timing first, then try changing the spring if it still stumbles.

Thanks for all of the responses. I have found one of my issues - a worn cam. The water pump started dripping and I had a small leak at the front of the intake. So, while repairing these things I noticed #2 intake lobe on my cam had a ridge on it and the machined surface looked different than the rest. I am going to order a new cam in the morning and go from there.