Possible Carburetor Issue

I have a 2007 Arctic Cat Prowler H1 with approximately 715 miles. When it reached approximately 600 miles it developed a bad mis, which is very noticable from the exhaust and the idle is very erratic, sometimes it's high and sometimes it wants to stall. It really get's bad with the change of altitude, to the point where one minute it will idle very high and the next minute you can't keep it running and it pops out the exhaust really bad. I thought that it was a fuel mixure problem, so I diassembled the carb and cleaned all the passages and jets, however, after reassembly it still has the same problem. I checked the valve settings and they are ok, changed the spark plug and that didn't make any difference. Checked for air leaks on the suction side and couldn't find any. It doesn't appear to be an ignition problem, spark is very strong and consistent. When you put the engine under a load to climb a hill or run it hard down the road, the engine smooths out and runs good, it just seems to be when it idles or in a no load situation. Cylinder compression is also good.

I sure would like to fix this problem, has anyone out there experienced this or something like this ?

Thank you