Several of us are in the front range area, mostly in the 6000' catagory. One of our members and a sponsor, bicycle engine kit, bike engine, bicycle engine, bicycle motor
has experimented at much higher elevations. You might consider contacting the owner, Duane, to see what he recommends for an engine that sees thinner air. You can naturally assume that you'll be dealing with a richer mixture due to the elevation. Raising the 'c' clip on the needle would be the first step Duane might have some other information to add. Good luck. Keep us posted.