Based on what you described, I would investigate whether the governor gear broke. It is inside the crankcase and is a major repair.
To do a test, tie the governor arm so it doesn't go full throttle before start. Start the engine, then slowly release the governor arm and see if the is any resistant force on the governor arm pulling the throttle shut to regulate the rpm. if the is none, there is a good chance the gear broke inside the engine.
To do a test, tie the governor arm so it doesn't go full throttle before start. Start the engine, then slowly release the governor arm and see if the is any resistant force on the governor arm pulling the throttle shut to regulate the rpm. if the is none, there is a good chance the gear broke inside the engine.
