The problem started as the throttle is snapped the engine coughs then powers up. When the throttle is rolled on it the power is all there!! Just when you need a quick snap it dies b4 accelerating. Does it at half throttle also. I cleaned the carb. Twice, air filter is clean, tried to adj. the air screw and put in a new plug. I even changed the accelerator pump. No change in problem. The new accelerator pump parts listing did not specify difference in the 4 different ones available, so the parts guy said order the first p/n, it should be the original one anyway. The new one came in with the number 3.7 on it. The one I took out of my bike is a 4.3. The throttle response was better but still has the snap cough. The parts guy wouldn't refund me the part for exchange for the 4.3. Tonight when I started it, it was hard to start. It took about 3 kicks for it to fire off then die. Did it about 7 times. I got it to stay running by giving it some gas. It sounded like crap then. It ran, popped and backfired repeating in that order as long as I kept some gas to it. The eng. RPM was erratic but would not idle. What's wrong??