Take the air cleaner off and look down the carb while you open the throttle. The accelerator pump should squirt a stream of gas like a water pistol. If your shooter is bad, it will stumble badly when it is cold. I'm not questioning your ability to rebuild the carb, but things can go wrong.
The accelerator pump squirts out gas just fine. The problem doesn't happen when I stomp on the gas pedal. It happens when I'm holding the gas pedal down to accelerate (i.e. after the accelerator pump is done doing it's job). Thanks for the suggestion though.
By the way, this problem started before I rebuilt the carburetor and continues after the rebuild. The carb needed the rebuild regardless (was leaking gasoline slowly at the seams), which is why I ventured down that path in the first place. Unfortunately it didn't resolve the problem.
