86 30HP Johnson Still Screaming (sort of)

shawnswan

Seaman
Joined
Jul 6, 2006
Messages
53
I posted earlier about not being able to go over a certain speed without the motor over revving and sounding like I was caught on weeds. The general concensous was that the prop was spun. I followed the instructions and marked the prop in relation to the shaft, ran it a few times and checked everytime, the marks never changed so not a spun prop. On my way home last night I noticed that the transom is a little soft and when I try to go fast the motor tips back slightly so I adjusted the motor so that when the boat is stationary the motor tips forward slightly, when I go fast the motor cowling is level with the boat. I only got to test this once but it seems to have worked. Does this make any sense? I obviously need a new transom. The only reason I can see this working is because with the old setup when the motor was tipping back I think the motor was pulling water from the surface and along with it air causing the motor to over rev.

Thanks.
Shawn
 

Cofe

Lieutenant Commander
Joined
Apr 23, 2009
Messages
1,883
Re: 86 30HP Johnson Still Screaming (sort of)

Yep it is called cavitation, when air is drawn into the prop. For optimum performance the plate above the propeller will just be at surface waterline at WOT. Adjust trim/tilt for optimum performance.
 
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