Here's my situation. I was enjoying a fast ride on my Sport 400 when it suddenly quit on me. It wouldn't start. I still had compression but not alot. When I took my machine apart I noticed an edge of my piston looked like it had been shaved down. A few weeks earlier I turned my air screw a half turn leaner. Prior to my last fateful ride I thoroughly cleaned my air filter (not stock; Twin Air). Can someone please tell me what happened, and the best way to go about fixing it?

 

You were leaning it out too much. The air screw was set to a leaner position, and the clean air filter allowed better air flow. The combination of the two must have made the machine a little too lean. I'm no 2-stroke expert, but that's what it sounds like to me.

 

What # main jet were you running at the time?

Was the needle jet in the stock position?

 

No jetting was done. Needle was in stock position. Thinking maybe something might have blocked my oil flow. Thinking of just scrapping my oil injector and mixing. Any thoughts?

 

Had the exact same problem with my 500 6x6 this summer. 297 miles on it! I think the oil carrier on the piston got clogged. One side rubbed the cylinder wall so much that it fused the rings into their grooves allowing blow-by. It stalled while I was riding and wouldn't start again. Costed about $250 for parts and getting the cylinder bored. Did the work with a friend so no labor included.