85 Johnson 15hp replacement

M

masterp

Petty Officer 3rd Class
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Sep 1, 2002
Messages
84
I own a 15hp johnson powering 14.5 deep v alluminum Grumman open bench type boat. I purchased the motor used in 94. Every now and then the motor will stall after extended trolling. After having several shops work on it, I was tolled that the compression on the cylinders didn't match. I had the fuel pump and internal lines replaced including primer bulb and tank. I'm thinking of just replacing it. It's the primary motor on the boat and I need it to be dependable. The motor weights 72 pounds. The tansom has been cut down to accommodate a short shaft so I don't want to put to much weight on it. Any suggestions would be appreciated.
 
clanton

clanton

Rear Admiral
Joined
Jul 9, 2001
Messages
4,876
Re: 85 Johnson 15hp replacement

A head gasket may cure the compression problem. Then check water flow at idle.
 
S

Solittle

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Apr 28, 2002
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Re: 85 Johnson 15hp replacement

Could you tell us what the values were on the compression check?
 
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masterp

Petty Officer 3rd Class
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Sep 1, 2002
Messages
84
Re: 85 Johnson 15hp replacement

I just pulled the paper work and the compression difference wasn't as bad as I had thought. #1 cylinder is at 85 psi and #2 is at 90. I don't see any mention of a timing check, but they did check the spark and change the plugs.
 
clanton

clanton

Rear Admiral
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Jul 9, 2001
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4,876
Re: 85 Johnson 15hp replacement

These engines have a problem with the upper water tube grommet, that restricts the water flow. One indication is top seal blown out of water pump housing. The others are overheat that new waterpump does not cure, low water pressure at tattle tale, blown head gasket.
 
JB

JB

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Messages
45,907
Re: 85 Johnson 15hp replacement

Hi Masterp.<br /><br />You said you do a lot of trolling. Did they decarbonize your engine? Your symptoms, including the compression numbers, suggest carbon to me.<br /><br />It is so easy to decarb that it would be a shame to replace a Johnny that is so young. Now if it were a '55 or '65 we might call it old. :)
 
M

masterp

Petty Officer 3rd Class
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Sep 1, 2002
Messages
84
Re: 85 Johnson 15hp replacement

I don't see anything on the paper work about decarbing. I'll give it a search and try it out thanks. I'm still a little worried about this stalling problem though.
 
M

masterp

Petty Officer 3rd Class
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Sep 1, 2002
Messages
84
Re: 85 Johnson 15hp replacement

Thanks Bear.....that's a really interesting link. I have a shop manual for the motor but not specifically for the 9.9 and 15hp.
 
D

DJ

Guest
Re: 85 Johnson 15hp replacement

Masterp,<br /><br />Decarb. the engine. I think you'll "wake it up".
 
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