Hi there can be a number of causes like stuck governor arm or the butterfly that goes through the carb sticking.
Another thing to look at is the carb itself - the butterfly inside the carb that reacts to the throttle is fixed with a small bolt on the the pin through the carb. These sometimes come undone so the engine will just race with no throttle control. To repair remove carb and refix with some loctite. The butterfly and bolt are normally lying in body of carb.
e park mowers, February 2009
