1957 Johnson 18hp.

[Ghg]

I have a 57 Johnson 18hp. It runs fine but when I try to push the throttle to full power it starts to cavitate or over revs but is ok again when I decrease throttle. It’s not jumping out of gear or anything. Just prior to that I got some rope tangled in the prop, just wondering if this caused some damage or just a coincidence. Is there a rubber hub on this prop?

 

[tphoyt]

I would guess it has a shear pin if its the original prop. Pop it off and see what find.

 

[racerone]

A 15" motor on a 20" transom ???----Or sounds like the rubber hub in the prop is loose.

 

[airshot]

Or...does he have a short shaft on a long shaft transom? Woops..already stated

 

[Ghg]

I’ll remove the prop to look at the shear pin, I wouldn’t think I would have any rotation if the shear pin was broke, the motor has been on the pontoon for 40 years, I don’t think it’s a issue with the transom height

 

[racerone]

OOPS----I guess I missed that fact in post #1 about it being mounted on the same boat for 40 years !!

 

[lindy46]

Spun prop hub?

 

[Ghg]

Did these 57 18hp. propellers have a rubber hub?

 

[F_R]

Yes they did/do, and that likely is the slipping problem
Is this a new problem? How long have you had this boat?

 

[racerone]

Post #3 clearly says to look at the rubber hub !!!

 

[Ghg]

Yes, new problem and have motor and boat for long time, I’m guessing it’s the rubber hub in the prop. I’ll check it out next time I get to the boat. Thank you everyone for your advice!

 

[racerone]

Mark the hub and prop.----Test run the boat.----Inspect marks to see if they have moved after a slipping ( ? ) event.