Re: 91 evenrude
we just bought a 91 pontoon with a 40 hp Evenrude, took her out ran fine for about 1 hour than started reving up with no prop in gear. does it have a clutch?
Not sure what that means...
Was it revving in gear and not going anywhere?
Was it just revving up with no throttle in neutral?
If it was the first it could be your prop hub. The prop is pressed on to the shaft with a rubber hub in between, when the hub goes out the engine will run but the prop will not spin.
On land put it in gear and try to turn the prop with your foot. If it slips you will know it is bad.
Next test is to mark both the center of the hub and the outer and run it in the water again and see if the marks still line up. If not its the hub.
Other things it could be are shift cable or problems in the lower unit.