Just a tip in case anyone else has had this trouble. My '07 WR450 was always hard to start if it had been sitting for a few weeks. I talked about it with a friend of mine who builds and tunes Superbikes and he suggested draining the float bowl. He said that gasoline these days goes bad quickly, especially in small amounts. Sure enough, I drained the float bowl, refilled it with gas from the tank and it started right up. Don't know if the ethanol content of the fuel has anything to do with it but the problem seems to be solved. FYI.