So, my friends sportsman 500 has a stumble at 2000 rpm. It seems like its lean, I cleaned the carb and its spotless. I turned out the fuel screw a 1/2 turn and pulled up the needle one notch but it stumbles at about 2000 to 2200. It seems to run better with the choke partially on. Those adjustments helped but it is very finacky especially when cold. Any other ideas that may help? I am not very good with vacuum carbs. It has about 10,000 miles could there be valve issues?

How's the battery? I have the same machine and would seem to run lean when I had a bad battery. Runs fine with a new one.

Check to see if the intake is clear. There usually is a piece of foam, glued to the underside of the plastis, right be the air intakes. Might be sucking it in a wee bit.

I think that the battery is weak so, we will try a new battery to see if that helps