This weekend a buddy of mine melted a piston. He rides a 02 xc500sp. The piston on the PTO side is the one that went. Right now I am not sure what caused it. I also ride an xc500sp and so does my brother and all three are setup exactly the same as for jetting and clutch setup. However when I pulled his plug I noticed that he was running a NGK BPR9ES. I run the stock plug Champion RN57YCC. As soon as I saw melted metal I pullled the plug on the other side. It looked good. Does anybody know how the BPR9ES compares to the RN57YCC? My first though was that the NGK is a hotter plug but I dont know. I forget the jet setting on the carb. The temp outside at the time was 16 to 20 degrees and I am located in Michigan don't know the elevation. Another question does anyone know why the PTO side is usually jetted richer then the other side? Any help would be great.