Fuel Screw Adjustment for Altitude


Have an 02 426 and it runs awesome at sea level.. Starts well, no bog, and too fast for me. So I have not done anything to the motor other than pipe and NoToil filter.

I am now often taking it up to around 6000 ft, and also ride at sea level - switching back and forth. It is ridable at altitude, just a rich stumble off of closed throttle.. Once it revs up, runs OK. Slower, yes, but since we are doing trails in the mountains, not a real problem.

I would rather not have to rejet every week for the trips up to the mountains.. Is there anybody that has had success just making adjustments to the fuel screw to get rid of some of the rich condition off idle?



Plan on the bike being rich at altitude. You can get away with a simple main jet change and leaning the fuel screw. Swapping the main jet is easy enough normally not requiring any disassembly of the bike, same goes for the fuel screw adjustment. Plan on going down one size on the main and 1/2-3/4 turn leaner on the fuel screw, approximately of course.

Change the main jet using a correction factor of .94 and lean the fuel screw 1/2 turn. 5 minute change, including digging out tools and jet box.

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