you have any mods; pipe, silencer, air box?

have you tore it down, cleaned the carb, rebuilt it with a new kit?

at that elevation you should be somwhere in this ballpark:
- air screw 1-1/4 turns out
- pilot #45
- needle 3rd clip from top (middle)
- main jet 190 (stock) 200 (aftermarket silencer) 210 (exhaust and air box lid removed)

after that it should idle fine if all is clean and operating properly