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1989 Johnson 90 hp

T

Tim Strub

New member
I have a 18 ft Starcraft with a 1989 Johnson 90 hp. The dealer told me that it would run at 5500 rpm. It ran at 4000 rpm and it was move at about 35 mph. I should have my gps out to make the speed is right. I took the vro system out. I have not take out the boat yet since I done that, so I do not know of that would change how the motor would at full power. What should be the speed and what should be the rpm at full power? I was the only person in the boat.
 
kimcrwbr1 said:
You may be able to get more speed out of it not much I would imagine. You need to confirm the rpm and the engine is running close to 100%. What elevation are you at is the prop correct for your boat. Less pitch will increase rpms but the prop is the last step is the tach correct the hull clean trim is good is it slow out of the hole you want max rpm for the engine to perform properly better hole shot and mid range economy. Sounds over propped to me if everything else is correct.
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I have the motor trim all the way down. This my first big boat that I have had. The last boat I had was 16 ft with a 15hp motor on back
 
you should get 5000 rpm out of that motor......i think it is rated for 5000=5500 but its hammering real good at 5000 and i would be happy with that...you want to get that rpm up.....its good for the motor......
 
agree with racer on compression....spark etc....you also may have a problem with the little roller(cam follower) that advances timing...it should be a steel roller covered by a fiberglass looking material....this material cracks and falls off(usually you find a piece of it laying down in bottom of lower motor cover) and then all you have is the steel following the cam and it advance timing but not enough....4000 is actually a little high with this problem but its worth a fast check...
 
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