Yamaha prop revs on its own

[robert1308]

I have a Yamaha 250hp 4 stroke with low hours. The prop has been revving up without throttle increase and it has not been pissing. As soon as this happened I shut it down. The gauges did not register overheating. What are the causes of these problems? What should I do?

[boats.net]

May have gotten grass or something wrapped around prop and or gearcase, prop hub may be slipping. May need water pump replaced.