I have a bone stock CRF50 that has always run like a snappy little tractor but suffered extremely poor performance at Gorman (5000 ? ft)last week. It was rediculously sluggish and only seemed to get up to about 2/3 revs. When I got back home (sea level) to examine it, it ran perfectly again. The only culprit that comes to mind is the altitude change. But I have never noticed such a huge power loss at different elevations before with any of the bikes I have owned. Could the altitude play that much of a role with the performance of the little CRF? I don't want to rejet because most of the usage is 0-1000 ft elevation. Would an aftermarket exhaust system help? Thanks!