with no load the engine will rev to 3200.On load it will only go to 2400.air filter ok new fuel filter fitted.new block 5 years ago with new piston etc.No smoke from exhaust.slow to pick up revs.Any suggestions please.
Unlikely to be prop problems since your engine isnt smoking. More likely to be lack of fuel ie partially blocked filter. Either way check out the obvious things like fuel supply, air filter etc.
If none of them have an effect, then check valve clearances and compression .
Sounds about right.... What did you expect. The poor engine is blasting leccy into a discharged battery, turning a dirty propeller and you may even have the boat tied up. Give it half a chance.