A buddy & I are riding up in CO these past 2 weeks. Saturday we moved from Lake City to Taylor park. I had to do some maintenance/tuning because I swamped my '06 crossing a stream. Anyway, my buddy's '03 was popping a little so we dropped his main from a 160 to a 158 and raised the clip on the needle one notch (from 3 to 4 from the bottom). After that the bike wouldn't start. It usually kicked over easily. Even though we didn't make much if a change, we went back to the original clip position and main. We finally got it started and tried to go riding. The bike would run like it did before but start stumbling and then die like when you need to go on reserve. It would need to sit a few minutes before it would start again. We went back to camp and pulled the bowl off thinking something was clogging the needle jet. It looked fine and the float assembly seems to function correctly. We also tried running with the gas cap loose thinking it might be vapor locking. If we run at a mild pace on the back roads, it'll go quite a bit. If we start running trails, not so much. Anyone have some ideas we can try? We've got two more days to ride and then it's back to the heat in Texas.