i have encountered the same problem. i live in sacramento, cal at about 52 ft. but do all my riding in the sierras. i found that i was always running too rich at altitude. this was compounded by my plans to ride paiute trail with elev. going about 12000 ft. first, i purchased the dyno jet kit. there have been complaints but i followed the exact directions for rejetting to 3000 ft. and the foreman went to 11500 ft. in utah. since then i installed the hmf pipe which leaned it out a little more. the dyno jet kit has multiple jets and redesigned needle that also is adjustable unlike the stock one.