I have a 2003 YZ450. I change the oil and clean the air filter religiously. I recently had the top end re-done, and everything seemed fine until I hit the 10 hour mark on the engine timer, now I am having problems with it again. On my last ride, it suddenly flamed out on me (stalled out on flat ground while I was giving it about 1/3 throttle with practically no load on the engine). When I tried to start it, I noticed that there seemed to be no compression for about six or eight kicks, then suddenly it was back to normal. I couldn't get it to re-light, so I decided to change the sparkplug (which looked fine). Again, it would kick through a bunch of times with no compression, then suddenly there was a TON of compression (I could barely move the kickstart). Then it would go back to normal (3 or 4 kicks with light compression, then normal TDC again). After messing with it for a while I finally got it started. Initially it ran ok, but on the way back in it lost power twice, wanting to stall out again. Since I was idling back in fourth I had some momentum going, and it would come back and run fine again for a while. When I got home, it was VERY hard to start, and I noticed that it would occasionally try to die out even while it was sitting on the stand, with no load on the engine. I completely cleaned out the carb (found a little gunk in one of the jets and thought "Aha!"), bolted it back together, and went riding again. It started up immediately, again seemed to run fine, but 5 minutes into the ride it started the same "die out/come back" crap. Unfortunately, I didn't make it all the way in before it completely flamed out on me again. After kicking for a while, I gave up and managed to get towed back in. So, now I am thinking it might have something to do with the automatic decompression? Has anyone else out there had something similar happen? I'm thinking about tearing into it to check things out ... any tips/suggestions? Thanks !!