Not sure where to look. Sounds almost like it backfired and damaged something perhaps a trip to YS Parts and Service will do it good.

My inital thought was the throttle barrel stop screw....This would cause the throttle barrel to leak and could give it some symptom like you are describing....but if this screw is still in place maybe there is some dirt or debris in the throttle barrel, fuel control slot or what we call the scroll. A piece of crap could be blocking this slot partially....when it at full power the dirt is out of the way but as it transitions back the debris is stuck in the slot or may attached to it somehow.


Troy Newman
Team YS