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"runs like a top up to about 4000 rpm and then acts like a rev limiter is kicking in..............carb size problem?
Over a hundred-thousand C3 vettes were produced with Rochester QuadraJet carb ... each one rated at approx 750 cfm. Not much info in your post, but if you have an HEI distributor, maybe you need a new ignition module ... the problem ain't due to carb size.
I currently run an edelbrock 750 with mildly built motor. It runs beautifully. However I did have a 750 that did exactly what you are saying. At first I thought it was the distributor, timing problem. But it turned out that an imperfection in the base of the carb was causing the secondaries to stick and then slam open which caused the car to do similar things. Good luck...