I'm having a new issue with my 2000 Xplorer 250. I've had it since it was new, and it has been great. The only work done to it since new was having the top end rebuilt 3 years ago. I live at around 700' elevation, in the upstate of SC. I've got a couple acres up in the mountains of NC, up around 3000' elevation. Recently I was riding a gravel forest service road; nothing crazy, but a gradual grade that is usually open to highway vehicles; any Honda Civic could make it up fine. The engine started kinda bogging, and stuttering and mid-throttle, and also noticed the engine was very hot. This was only about 2-3 miles since firing it up, and I figured that it might be some new problem, because the quad's getting old, etc, and should just go home, which it did make it back to. Today, back home at 700', I took it out for a test run, and ran it pretty hard for longer than I ran it up in the mountains; no problems at all. No sputtering, bogging, excessive heat; nothing. So that got me thinking; owning carbureted motorcycles in the past, and having them run fine here (700'), then driving them up to say, the Blue Ridge Parkway, and they would try to stall while at an idle at say, 5000', got me thinking. Do I need to like re-jet my carb or something? The engine is completely stock, btw. I figured I'd post this up on here before taking it to a shop. Cheers.