hi, ive got a 97 yz250. ever since this winter its has had problems with not having a lot of power. the reeds are fine, the carb is clean, and its jetted correctly. it was fine before i put it away for the winter but when i went to take it out, it will run fine for five minutes and then it will seem like it has no power and it wont idle as well. then i'll let it sit for a day or two. it will run fine with lots of power for about five minutes and then all of the sudden it has absolutely no power. its not like it slowly loses power, its all of the sudden. so i went and rebuilt the top end and i soaked and cleaned the powervalve. i put it all back together and it seemed to be fixed. i broke in the motor properly and i was doing some riding at a buddies track and after 5 hours of ride time it happened again. it seems like the longer i let the bike sit, the longer it will run fine before taking a crap. even when it runs crappy it starts fine if i give it a little throttle. oh and by the way, its not the spark plug wire or ignition coil because i repaced that. any ideas??