Johnson 88 max rpm's

[surrender]

This is posted in the prop section also. 1996 Johnson 88 special.

Ran boat today after raising motor. Took a little longer to get out of the hole but it was adaquate if not pretty good. Tach only showed around 5150 top end and it would go up if I trimmed out the motor but boat would porpoise real bad as rpm's went up and boat got higher. Got to 5250 or so and boat would almost bounce and rpm's would surge and almost over rev. Think motor would be happy to turn up if you could hold it from bouncing. Sounds good. Checked all spark plugs after getting home all look about the same. Tannish electrode, darker at insulator but no signs of fouling. Dont think I'll do much more except bring an old electric tach/dwell meter that is supposed to be accurate and verify the teleflex tach. Maybe a set of tabs if I come across some used ones.

Any thoughts? Boat is an older McKee craft 17 offshore fisherman. Prop is a 13 3/8 X 17 Stainless. Motor has one of those "whale tails" on it. Seems to jump out pretty good.

 

[tashasdaddy]

Re: Johnson 88 max rpm's

5600-5800 would be nice for top end. that way it will not lug at lower speeds. a Set of Nauticus Smart Tabs, will get you out of the hole faster, and help tremendously with the porpoising. some weight in the bow will help also.

 

[surrender]

Re: Johnson 88 max rpm's

I told my buddy to go sit in the bow. It was about 35 with the wind chill. He stayed behind the windshield. i really think if I got tabs and got rid of the tail(lose the high speed drag) the boat would turn up to 5500 at least. Dont think I want to change props just yet. gonna find some extra cash and put some tabs on first.

 

[wilde1j]

Re: Johnson 88 max rpm's

Make sure the setup is right before spending money on a prop. Have you tried raising the motor up a hole? If the AV plate is under water @ WOT you can surely come up one or two holes. The AV plate should be just out of the water and hard turns should cause excessive cavitation when you get the "X" dimension right. You will gain some RPM and top end speed as well. Also experiment with the trim as well to optimize speed. When you finish all that and RPM is still below 5800, drop a couple of inches in pitch.

 

[surrender]

Re: Johnson 88 max rpm's

Wild,
I raised motor two holes over the week end and boat seemed to be faster and rpms sounded like she was pretty wound out but tach only showed maybe a 150 rpm increase after the raise. prop does try to break free in sharp high speed turns so I dont think I'll go any higher. Going to run it again and verify accuaracy of tach and have friend ride up front and try to get boat trimmed out and see where it ends up. Just wants to porpoise real bad when you trim out. Rpms will rise if you can stand the bow bouncing. not to worried about that as I wont run at WOT just want to see if it is set up right.