With track off ground revs up and track moves freely with no issues, put it on the ground bogs at 4000 rpm's and will not get up to enough rpm's to fully engage clutch. carburetors cleaned 3 times, belt changed, fuel lines/filters in tank changed, spark plugs changed, fresh prem gasoline, HAC changed, compression checked 140 in each cylinder. Starts on first pull. One thing I have noticed is when adjusting carbs the idle screw has to be turned all the way in and bottomed out to get the idle up to 1600. Any suggestions?