25 HP Johnson died

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Dialtone75

Cadet
Joined
Jul 17, 2009
Messages
13
I was flying along on my local river a few weeks ago at top speed all alone when my boat came to a sudden crawl. When I put it in neutral it revs fine. Put it in gear and will not rev up. Prop turns and the water coming out of the motor was hot, but not too hot to touch. It starts perfectly but again wont get up past a crawl. I started to take the lower unit apart but everything is turning fine. A couple people said fried piston ring, while some others have said bad bearing in lower unit. Thoughts on how to determine which area to investigate?
 
lindy46

lindy46

Captain
Joined
Nov 27, 2008
Messages
3,886
Re: 25 HP Johnson died

What year motor? When did you last chage impeller? How is spark?
 
jacksoldoutboards

jacksoldoutboards

Seaman Apprentice
Joined
May 28, 2009
Messages
40
Re: 25 HP Johnson died

Possibly losing a coil or condenser. Does it have a pressurized gas tank? Possibly weak fuel pump pressure? I wouldnt pull the lower unit yet if it has good water discharge at idle. (At high speeds, the water pump is just along for the ride - because the motor gets water forced through it)
A few checks to do yet and I would start with ignition and fuel first.
 
D

Dialtone75

Cadet
Joined
Jul 17, 2009
Messages
13
Re: 25 HP Johnson died

It is a 1969 motor. I did a compression check yesterday. Both cylinders were above 100 psi and matched each other. Impeller is new. Water is pumping fine. While taking the lower unit off I checked the impeller and it still looks new. As I said it starts great and idles fine. Spark looks strong. I mean just watching the grounded out plugs while pulling it. The fuel tank is a standard 6 gallon metal tank.
 
tashasdaddy

tashasdaddy

Honorary Moderator Emeritus
Joined
Nov 11, 2005
Messages
51,019
Re: 25 HP Johnson died

if all you say is good, then carbs, read ethanol, and carb cleaning in the TOP SECRET FILE.
 
F

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,195
Re: 25 HP Johnson died

It is a story as old as twin cylinder motors themselves. I say it is running on one cylinder. Remove and ground the spark plug wires one at a time, and see how it runs. Betcha it won't make any difference with one removed, but won't run at all with the other one removed. That is the good one.
 
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