Try to turn the knob at the top of the choke shaft on the carb when you have the engine running and this choke lever knob is pushed down try to turn this knob left or right.. Turn left to idle down or right to raise idle up.. This works on most 2stroke race bikes but 4wheelers have been known to have this choke lever knob just spin when you try to turn the knob and is not an idle adjuster if so then last suggestion to idle down is adjusting your throttle cable to loosen up a bit approximately 1/8" inch either at the top of the carb at that end of the throttle cable or loosen at the throttle lever end.. If your throttle lever is re-adjusted a bit to make up for your high rpm and loosen the tension a bit this may be enough to accomplish the task.. Good luck
