Problem...

Ok, so I am at the point where I need to act like I have never learned anything about engines, tuning, etc. My car has an issue and I cannot for the life of me figure it out.

Specs: 340, X heads, Edelbrock LD340 intake, 650 Speed Demon, 3200 stall converter, 727, 8 3/4 with a 3.91 Sure Grip. It is in a Duster that weighs around 3200 lbs. The cam is aftermarket, but the exact specs aren't known. It has electronic ignition, new plugs/wires/brass cap and rotor. I removed the power brakes and went to manual brakes, the water pump is driven by an electric motor and it has an electric fan. I am using a stock mechanical fuel pump, all new fuel lines and a fuel cell. No air filter at the moment.

The issue is this: The motor idles fine (timing set at 10 btdc) and runs great at idle, obviously firing on all 8. I have my idle set at about 1050 rpm. The problem occurs when you mash the throttle from an idle or with a previous load on it (i.e. staging, etc). The motor will not rev up for the life of it without a horrible stumble and then it likes to puff back up through the carburetor. The vacuum advance is working, as you rev it up slowly, you can see it advancing like it should, but it will only rev up slow. If you floor it, it nearly shuts off and then comes on like a bat out of hell.

Throw out any possible ideas, or if you need other information, let me know, and I'll get it to you. Thanks in advance.