The last time I mowed the engine all of a sudden started running very very fast. The mower ran out of gas almost simultaneously. My husband replaced the fuel line after he discovered it was leaking. He felt that the reason the engine had run too fast was because it had been drawing too much air. The engine nows runs well and starts well until the blades are engaged and then it runs too fast and has to be throttled back. It also has odd high pitched sound. Does anyone out there have a clue as to what may be causing this?