Yamaha 4HP Help

[muddypete]

Can anybody out there help
I have a 2002 yamaha 4hp 4 stroke. Starts fine but when I get up to a certain number of revs it begins to overrev. I thought it may be cavitation so lifted the motor up a cog to no avail. Have shifted gear to both the back and front to try to alter the centre of gravity.
With the motor out of the water I can spin the prop in neutral in reverse the prop can be turned and the piston goes up and down In forward however the prop turns fairly freely with a clicking noise Could this be a worn cog or gear somewhere? My normal servicing outlet still hasn't returned my call (5 days!!!!)
Regards
Muddypete

[FNQCairns]

Doesn't sound like a gear problem, what is it fitted to and are you on the plane when it happens or still barging along pushing lots of water?

If on the plane then it's probably not mechanical, if you are still barging along it could be mechanical or physical.

Plastic prop? overall sounds like air (ventilation) drop the engine down to past where it was originally and/or post a pic of the transom and the engine in the down position.

cheers fnq

[muddypete]

Thanks FNQ
The boat is an old aluminium 12 footer with an aluminium prop
recently had the boat upside down in the shed to repair a couple of small leaks but motor refitted in the usual place and at the usual height
The boat doesnt usually get on the plane
I have to pick up the crab pots this afternoon so may try adjusting the height of the motor to see if I can get any improvement.
regards
muddypete

[FNQCairns]

yeah Pete try lowering the engine to decrease ventilation as a start in an effort to see if that changes anything, raising it will usually increase the likelihood of air getting access to the prop.

cheers fnq