2001 Yamaha 15hp 4-Stroke

AlexKemp52

Cadet
Joined
Mar 11, 2017
Messages
7
I have been having an issue with my outboard for sometime and have not been able to diagnose the exact issue, so hopefully with this post it will point me in the right direction.

My engine seems to knock at a high rpm without an increase in speed. The knock starts off slow, but when I increase the RPMs the knock gets extremely rapid after a certain point. I back off the throttle and the knock goes away immediately but the speed stays the same.

I took it into a shop to get a diagnosis and they simply told me that their was too much oil in the engine and that it should fix the problem... Well the issue wasn't fixed so I spent $150 on an oil change. There wasn't any metal flakes in the oil and compression is good.

The guy I bought the engine from had run it dry and completely melted the impeller in the water housing unit so I had to replace that (easy fix) before I even took her out on the water. I believe that he overheated the motor and created this issue.

I have done some research and think I am not getting any power from one of the pistons, but I am not sure.

I am at the point where I am about to take the whole damn thing apart and check the guts of it.

Any help would be greatly appreciated!
 

99yam40

Fleet Admiral
Joined
Sep 7, 2008
Messages
9,212
leak down test should show if there is a problem with cylinders sealing properly.
bad gas, ecessive carbon, or out of time can cause knocks
 
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