Hello, Forum, I have been reading this forum for a while but haven't written in until now. I have a 95 xcr 600 that I just aquired. Well I just melted it down 2nd time the middle cyl. Not real bad. But strange. the other cyls have piston wash that looks rich. And the piston that melted is eroded on the exhaust side of the piston not to the ring but close. I have wrenched on Atv's for a long time and melted several down trying to get that last bit of power you know lean is mean. But this thing runs great around the house but get out on a long snowy road and melt down city. When I first got it the air box was gutted and did not have any foam between the hood and the air box but it was jetted really fat. Since then the air box is back to stock with new foam between hood. jetting is two up from stock on the main and everything else is at stock settings. 10m weights with a blue spring in the primary with top rpm at 8900 secondary is a 40/38 with a blue spring set at #4. also it has psi pipes. My question is might I have a combination problem. could the timing be advanced with a tight secondary putting high load on the engine. Or am I just reading to much into this and it's just lean jetting.