70hp Johnson, no power under load.

[deputydawg]

I have a 1977 Johnson 70hp on a 1977 15' Tri Hull. I had water in a cylinder in the spring. Ended up replacing all gaskets in the power head. This solved that problem. It had been sitting for many many years and gaskets dried up. The cylinder walls looked excelent, everything measured perfect with a micrometer, no cylinder ridge, excelent compression. While I did this I replaced a broken prop with one I picked up on sale. The new prop has more pitch than the old prop. On the water it ran great with one passenger. When I loaded up with 4 people in the boat it would not reach WOT. It just had no power until I kicked 2 people out. Is this possibly too much pitch on the prop? There are no markings on the prop so I don't know what I have. I am selling the boat and want to make sure I am honest with the buyer.

 

[DJ]

Re: 70hp Johnson, no power under load.

That engine needs to be able to turn at least 5500 rpm at wide open throttle.<br /><br />If not, you are lugging it and it WILL die.