I have a '99 MXZ 500. It wasn't running good at high rpm and was low on compression in the right cylinder. I took the head off and the right piston was burned bad, especially on the exaust side. It was actually burned down to the top ring. The electrode on a spark plug that I took out of this cylinder a week ago was pretty much burned off too. The left piston had a divot burned in the middle about as big around as a nickel but not too deep. I can't figure out why it would be so hot. I am getting it fixed but I don't want it to happen again. I think it's getting enough oil because the cylinder walls are still perfectly smooth despite the pistons getting burned. Also, it only has 2000 miles on it.

mayby you were running it too lean on a cold day.
that would fry it.

sound like too lean to me.

Yup sounds like a lean burn to me too. Go up a couple of sizes on the Main Jets and one size on the pilot jet