When you move the throttle lever,are you sure the linkage is moving on the engine?Sometimes the locknut on the throttle lever will come loose and the throttle doesn't operate correctly.Something to check for.
Throttle is set at idle and does not change RPM even if you move it through the full length of travel. Just quits after racing at 3000 rpm for about 30 seconds. Can't slow it down w/o turning off key.