Update on 93 Johnson 90

[dozerII]

Can't find the originonal thread it was too long ago. 1984 Starcraft 16ft SS 93 Johnson 90hp. Had trouble with the tach not giving me accurate readings. Replaced the regulator rectifier and finally got the boat out last week end. I was told in the last post to raise the motor one hole on the transom to get a little more rpm, this put the anti cavatation plate 2 inches above the bottom of the hull. Tried this but it just blows out on small turns and crossing wakes. It is now running at 4900 rpm at 36 mph wot with a 14 X 17 aluminum OMC prop, What recomendations would you have to raise the rpm and speed? I live in an area with no access to parts or props so must buy them through I boats, so don't want to have to buy too many.
Thanks Glen

 

[steelespike]

Re: Update on 93 Johnson 90

Typically a 90 on a boat similar to yours would run a 17" prop. turning over 5,000 rpm. You might be sure the throttle plates open all the way and be sure the motor is in excellent tune a 15 would add "about" 400 rpm.
A prop with a little cup would resist ventilation.

 

[dozerII]

Re: Update on 93 Johnson 90

Thanks Steelespike, I checked the throttle plates, and they are good, The motor only has 4 hours running time on it since a rebuild at a marine shop, I am still running 25/1 fuel mix, and it is running great other than the smoke from the fuel mix.
Glen