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My 302 idles great, and does great when I really hit it, but at mid throttle it runs rough. I have to let off the gas so there is no load on it or give it more gas so that there is a real load on it to get it to run right. I've rebuilt the carburetor, and replaced the fuel filter, points, condensor, distributor cap, plugs, plug wires, coil. The fuel pump is good.
This problem just popped up all of a sudden, one day I was driving it and everything was fine, the next it had this problem.
I could be way off; but motor mounts have cause this reaction in the past for me and a buddy of mine one time. Also at high end seem fuel pumps to lose their capacity to push fuel.
But i'm sure its something else. Just trying to get ya to check your motor mounts.
1. Fuel pressure while driving at the speed it occurs- possible fuel pump
2. A small particle might have found it's way into the carb fuel passages
3. Power valve/accelorator pump might not be adjusted right or have a pinhole in the diaphram
Did you replace the power valve when you rebuilt the carb? If so, was it an exact duplicate? Did it happen right after rebuilt? If its a Holley carb, the power valve is known to blow out very easily with a simple back fire. There is a "power valve protection kit" offered from Holley or Summit. Hope this helps!!