I have a 2002 XC 800 with the SLP performance edition package, SLP single pipe and a SLP high flow air box mod. The piston has about 200 miles on it and most of them coming from 1/4 mile drag races. Does the piston look lean? I have never seen a mark (almost wash) all around the piston. The exhaust side is on the bottom of the picture. I'm currently running 500 main jet with the TPS set at 4. It was set at 4.2 but I thought maybe that was causing the weird burn on the piston. SLP recommends 620's down to 0 deg and I have been running 500 but maybe that is too low. Is SLP that far off on there jetting specs?
What does everyone think?

Click to view attachment

i see some wash up where the intake ports are. that my friends looks like nirvana. I wouldnt run it any colder than what you were at, unless you richen up your jetting

the piston wash looks fine BUT How did you shut off the motor and get the piston out ? Piston wash should be checked after a 1/2 mile run , hit the kill switch with it still opened up and pulling. coast to a stop then look at your wash! this piston I am sure has some idle time on it.... the same thing needs to be done in the midrange , run it click it off under load then look at washat 1/3 trottle to see how the needle setting is!