Johnson 40 is weak

[dnohe]

Recently bought my Father in laws 17 foot Key West. It came with a 91 Johnson 40. The engine runs good and has good service history. My question is that she struggles to get the boat moving at top speed with 3 or more people in the boat. With 3 people in the boat she runs WOT at 4000rpms, 2 people 4500 rpms and with just myself, will run just over 5000 rpm. Is this normal for a 40 on a 17footer? She will never plane off and reach top speed with 3 or more. With 2 it takes a while, but will plane off eventually and reach top speed.

Is this just a cause of the boat being completely underpowered by the engine or do I have some other underlying issue. I would anticipate that the WOT rpms would remain consistent regardless of weight on the boat.

Any suggestions are greatly appreciated
Dean

 

[tashasdaddy]

Re: Johnson 40 is weak

you are grossly under powered. i would guess that boat is rated in the 90 -100 hp range. look at the capacity plate on the boat. anything under 70% of the rateing is going to be underpowered. you either need to change the prop, and accept what you have, to get the rpms up. as you are lugging that motor, and that can do major damage to it. really suggest selling it, and repowering.

 

[Silvertip]

Re: Johnson 40 is weak

Agreed. You need double the HP on that boat with those loads. I know -- I've been there.

 

[grid]

Re: Johnson 40 is weak

You could try another father-in-law, too. Took me 3 tries to get a good one.