I start out and motor runs fine . Go several hundred yards full throttle and it drops to running like it's running on one cyclinder or jumps (cuts out). I can kill motor and restart it runs fine till you open it up and run a short distance. Sometimes it will run 1/2 throttle with no problem for several minutes. It's mainly on top end that causes the motor to cut down. But runs fine to kill and restart ? Could this be caused by fuel or by spark from electrical system ?