John , externally it looks as it should , when not running the butterfly should be in the wide open position , when engine starts , it should then govern down. When you have it running , can you feel any manual resistance on the govenor rod , in other words feel it trying to shut down , if you can’t , it could be an internal problem with the govenor weights.
One other point , have you removed the linkage from the govenor shaft , and not refitted in the same position.
Andy.