1970 merc 115hp issues??

[hoofbite]

Hey folks, so here's the deal bought a used merc. Thing starts great idles great. In the tank in the driveway revs up beatifully, but under load only gets 18mph and Around 3200rpm. So weighed the boat with trailer and motor boat weight estimate around 900-950lbs for an ol 19ft trihull so I don't think it's water logged??? Any thoughts on where to start? As far as trouble shooting goes?

Thanks

 

[Chris1956]

Re: 1970 merc 115hp issues??

18 MPH at 3200 RPM is a strange combination. What pitch prop do you have?

Check compression, and see if any of the spark plug wires are arcing to ground. It sounds like you have a low pitch prop or a damaged prop, and are not running on all six cylinders.