Took the boys up riding in an area we've never been and can only imagine the altitude was about 2000 to 3000 ft. My son's alphasports 90 with a 54mm kit/uni filter/120 main jet/Technigas exhaust and clutch work did not run well. Quad did not even reach top rpm! Thought to myself, here we go again with this quad but when we got home, I guess around 500ft elevation. cleaned up the quad and drove it, and it was running like a champ again. Any one have any suggestions?

 

Did you notice if it was running rich, black smoke coming out the exhaust? My first guess is the setup you have
was just to rich. I'm at 5100 ft and all our ridding is from 4500 and up. All of our machines are jetted so we are lean
at the lower levels we ride at. When we are at 10000 ft the machines are still running good. Going from 500ft to 3000ft will have a large effect on the fuel mixture.