Need help troubleshooting an 85 johnson 15hp

Khenders

Seaman Apprentice
Joined
Jun 3, 2007
Messages
38
I have a 85 Jonhson 15hp (J15RCOB) with low compression (60 & 70, spec is ~115) and low flow out the tell-tale. I have already replaced the impeller, which made a small improvement in the tell-tale flow.

I have receive mixed advice on decarbing and I am leaning towards not doing it as the compression appears to be coupled with a water/cooling problem.

Here's my deduction...the older impeller ran the engine a bit warm resulting in a blown head gasket. Possible cause...the grommet on the upper end of the water line is dislodged.

From looking at the engine it does not appear difficult to replace the head gasket. But I do not want to go through the effort without correcting the cause. Am I over-simplifying the gasket job? How difficult is it to replace the grommet? Any other possibilies that I should investigate?

Thanks for your help, Ken
 

mikesea

Lieutenant Commander
Joined
Oct 1, 2006
Messages
1,830
Re: Need help troubleshooting an 85 johnson 15hp

to replace the grommet,the powerhead neads to come off,its not as hard as you may thing,especially if you dont have trouble with stuck bolts,I have posted a trick,sometimes this helps with the grommet prob.take a wire clothes hanger,straiten a piece long enough to go up the water tube to the powerhead,take a hammer and smash one end of the wire and grind a cutting edge ,you can then heat the cutting edge and quickly cool it to harder it,put it into a cordless drill and carefully ,slowly let it cut a passage through the collapsed grommet,I have done it sucessfully many times for people that didnt want spend labor for removing a powerhead with stuck bolts,but again,if you are somewhat handy,removing the powerhead isnt that bad,if you chose to do it,the hardest part is dealing with starter cord,you remove the center bolt,lifting as you unscrew,once loose,put a nut on the bolt to hold it all together .I also used zip ties,the spring inside can become a heck of a mess ,when you change the head gasket,take a piece of 80 grit wet and dry sandpaper lay it on a peice of glass or marble and rub the head on it,do it a few times then look to see if and how bad its warped,you can probably get it strait by continuing the process
 

Khenders

Seaman Apprentice
Joined
Jun 3, 2007
Messages
38
Re: Need help troubleshooting an 85 johnson 15hp

Thanks, Mike
Does anyone have an expolded diagram of an 85 Johnson 15hp?
 
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