As suggested before, check your carb for wide open with someone else mashing the pedal to the floor. If that's ok, check your fuel delivery system. Sounds like its running out of fuel. Could be as easy as a fuel gauge not reading correctly and not enough fuel in the gas tank (that happened to me at the Drag strip once). If you have enough gas in the tank, then check the fuel delivery system. Fuel pump pressure and delivery rate, possible clogged fuel filter, check to see if the pickup in the fuel tank has a sock filter that is collapsed or clogged up. Make sure you don't have too much rubber fuel line on the suction side of the fuel pump which might collapse as the pump suction increases as the rpm increases. Just a few suggestions here as you did not say there were any popping issues etc. in your initial statement concerning the problem. If it just noses over and doesn't pull and it did before, that's where I'd look.
Good Luck.
Bogusracer
