2000 Johnson Motor Slipping

[KEGG]

I replaced a 1972 25hp. Johnson motor with a 2000 25 hp. motor. Both motors have 15 inch shafts lower unit. The new motor slips and I thought it was the prop; however, I have tried several props and it still does it. I have also adjusted the trim. The roblem is while going down the lake at full throttle the prop will start to slip. The motor revs up and the boat slows down and sets in the water. As long as you hold the throttle wide open the prop slips. Let off the throttle and the boat will take back off. The new motor sits on the same boat, a 16ft. john boat, as the old motor and the old motor works fine. Any suggestions would be greatly appreciated!

 

[12Footer]

Re: 2000 Johnson Motor Slipping

It may be cavitation..Any air that gets to the water the prop is suposed to munch on, and you'll get a slipping sensation.<br />The cavitation plates, (the fins above the prop on the lower unit), should be below or even with the transom.<br />Also, look at the hull of the boat, and make sure no curves,tranducers,ropes or plates are introducing air into that water in front of the prop.