Probably a stuck governor vane and has been run that way for too long.
I would at least pull the cowl off and check the governor moves very freely - I have had to remove the flag and file a bit off the bottom of the bolt hole to stop it bottoming out on the coil (plastic expands with age). Check the throttle butterfly moves freely - could just be a buggered spring
Was the tapping from the loose axles? Or rod knock tap
