Take off your aircleaner and look down into the carby. There's a little scoop looking piece of metal that sits under the secondary butterfly thats supposed to direct air/fuel more efficciently into the manifold.

The part can wear causing it to slide forwards and either block the butterfly from opening properly or jam it wide open(much more dangerous).

If you cant see it, pop your carby off(4 bolts) and check it out. If it is loose just epoxy that mofo in place.