Rode Kennedy Meadows this weekend and had a problem on my previously rock solid 00 WR400. Adjusted the jetting for altitude 6000-9000 ft per JD specs (worked perfect last year). Went to start the bike and nothing. Bump started it and it ran but it would not idle, still could not kick start it. After 2 laps of this the bike lost compression. I could kick it all the way through with very little resistance. I figured I had a stuck valve or possibly a peice of sand, grit in one of the valve seats from taking the carb on and off. Checked the valve clearances and all seemed to be okay but the bike would not run or start on its own untill i brought the jetting back down to the 3000-6000 ft settings with the fuel screw 2 turns out. I had to set the idle very high to keep the bike from quitting and it still seemed to have a lean pop to it. Anyone have any ideas as to what is going on here? Anybody have stuck valves before?