briggs+stratton generator?

The govenor mechanism is either mal-adjusted, or stuck (more likely). Check that the govenor arm moves freely. Observe it while someone starts the engine. It should move from 'wide open' when at rest to some point at which the engine runs steadily at 3000 RPM (assuming 50Hz output). If there's no movement, it's either broken or stuck. If there is some movement, check that the spring isn't caught up/twisted. After that, you'll have to start pulling it apart to see where the problem lies. Prodedure will differ depending on engine model.

Phil Saunders
March 2009