you should check the jetting at WOT. do a plug test in that circuit. that means put the wheeler on the road in 2nd gear and hold the throttle all the way open. then hit the killswitch and pull in the clutch at the same time. don't let the engine pull the wheeler at all. then pull the plug and check for jetting condition. you will also need to check the plug after idle to check jetting at pilot.
also a compression check is highly recommended. if you've got some leakage in the rings, that could cause your white smoke. the reeds are another really likely culprit. if they're bend or cracked, they won't snap shut like they're supposed to and will not give the valving resistance necessary for engine control via the throttle.
That has nothing to do with idle. And the ring comment makes no sense at all. That only pertains to four strokes. Anyways, what is the difference in elevation between the two locations? Re jetting may be necessary. The rev hanging is usually due to a lean condition.
Try this sequence first; Turn your idle all the way down.Then start it and keep it running with the throttle. At the same time adjust your air screw until it feels like it's running it's smoothest. Now turn your Idle back up and see if you can get it to idle. If that doesn't work, pull off your carb and make sure the float is level if you haven't done that already. You can also check for a broken/ cracked reed at this time. I'm willing to bet that will cure or point out your problem.