Had this problem after i had redone my whole shee and it ended up being there is a little switch under the fuel tank and when it is let out it stops sending spark so all its doing is dumping fuel with very little spark, mine would sit there and idle and if you gave it any throttle at all it would just make a horrible noise, sounded like a machine gun going off, and all we did was just follow the wire back and unplug it, somone had actually put a plug over the switch and taped it and it must of worked its way lose, and i had ran it like that for about 4 yrs with no problem at all, hope this helps ya out.