sounds like an accellerator pump problem to me. Either the pump is not working, or it's just not squirting enough juice into the carb. To check this; pull off your air cleaner and quickly open the throttle. If you see a squirt of gas into the venturi, then the pump is fine and you might need to look somewhere else. If no gas squirts in, you have a bad accellerator pump and need to replace it.