I have a 1999 Polaris Trailblazer 250 with a Hot Seat Pipe and clutch kit, K&N filter and carb jetted for those mods. The quad recently lost all compression, I tore the engine down and when I got to the piston there was a small hole through the crown on the exhaust side. Does anyone know what could have caused this and how I can avoid doing this damage in the future? Any help would be appreciated.

 

What kind of riding were you doing while this happened? I have seen this occur on several two strokes that had been run long distances while at wide open throttle. On a two stroke the exhaust side of the piston always gets hotter than the intake side. A couple of opinions on why this happened was that the jetting was just a little on the lean side, not enough to make the motor run badly, but just enough to burn the piston on a long stretch, or a fuel mixture problem could have caused this also.