Was mowing lot next door and suddenly the motor just starts racing. I shut it down and it took a while to shut off. I started back up but the motor is still racing at top speed pretty much no matter what position throttle cable is in. Throttle cable seems to be operating properly. It's obviously getting gas as I can start it, but the motor just races even with throttle full close, where it would normally sputter as it runs, it just races now. What else can I check?