Whereabouts in Colorado? I used to ride a KDX220 (I'm told its a very similar feeling engine, designed in the same time frame) at altitude from Denver to 12,000 ft. I try to not be too picky on jetting but always switched to one size smaller on the main at 9,000 ft and above where it became a boggy turd. I'd use the 17 mm float bolt on the bottom and reach up in there blindly with a 6mm socket to get the main out. 7 minute procedure for a better running bike! Just a guess, but it seems like your main jet is off, possibly in combo with the needle position - I assume the needle position is adjustable? When in need of jetting, I'd pull the offending jet and take it to the parts store to get a match. Regarding Air leak: Get the bike up to temp and idling smooth as possible. Go around the carb, base gasket, and all around the intake with starting fluid. If there is a leak it will suck in the starting fluid and the idle will jump. I'd love to take a look at the bike if you're somewhere nearby and don't mind me fiddling with it a bit? I'm sort of interested in owning one and would like a good look before discussion with the CFO!