Mercruiser 120 help
 

I have a 1978 19' Grady White with a Mercruiser 120. The boat is very heavy and that little engine just barely gets it around. I'm looking for suggestions/ideas to get a little more umph out of it. I'd like to avoid spending too much though so a new engine/outdrive is probably out of my league. The engine runs nearly perfect now but it's just not strong enough. I've got a new prop and have already put electronic ignition on it. I had 4 adults and 3 kids on it the other day and it couldn't even get on plane. The former owner put a hydrofoil on it. He said it helps it plane but creates a lot of drag.

Have you tried a prop with a different pitch?

Yes, I think I've got the right one. It tachs out at 4200 rpm at WOT. (assuming I'm not overloaded)

I'm not sure what to tell you. If it's trailered, make sure the hull is cleaned and waxed. That will help reduce drag. Growth on the hull will really slow you down. If the boat has foam in the hull, it could be waterlogged, adding lots of weight and slowing you down. If you've got the boat trailered, and find water in the bilge while it's parked, it could be water seeping from the foam.

Are you able to adjust the pitch of the motor instead of the prop. It might be something different to try, my father has 65 Hp Merc his did a lot better once we pitch it different. I'm not sure what is right or wrong, but it seem to help.

i am afraid it is underpowered
 

trim tabs would help........but your root problem is the boat is underpowered. There is really no bolt on horsepower for that engine. Just make sure it runs up to the top of the rpm range with a light load in the boat

Put NOS on it. If you don't want to do that, I hear the decals alone give you a 50hp boost ;)

Lol a nitrous powered family boat, that's a good one. But yea the boat is underpowered, nothing to do except lighten the boat or get a engine with enough power.

about your mercruiser engine
 

Here are some tips on how to improve the performance our of your mercruiser marine engine

http://www.perfprotech.com/store/art...ical-tips.aspx