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Thread: low compression

  1. #1
    Join Date
    Oct 2007
    Location
    woodstock, new york, usa
    Posts
    69

    Default low compression

    85hp merc sat for 3 years. Compression was good when stored(125) Now at 50psi. Is there anything that can be done without having to tear apart? Thanks Bill

  2. #2
    Join Date
    Jun 2006
    Location
    Claremore, Oklahoma, USA
    Posts
    364

    Default Re: low compression

    Go to Walmart and buy some Seafoam in the automotive section. Squirt a few ounces in each cylinder or more and let it sit for a couple of hours or so. Recheck compression. You may have to repeat a few times.

    The rings are probably stuck form sitting so long.

    When you get it running mix Seafoam with your fuel/oil mixture for a tank or two to clean the motor out good.
    Bill

  3. #3

    Default Re: low compression

    So I have good compression in 2 cylinders at 1:18 each and the other two I have 95 do you think the seafoam thing might be an advantage to me

  4. #4

    Default Re: low compression

    Quote Originally Posted by Willie23 View Post
    So I have good compression in 2 cylinders at 1:18 each and the other two I have 95 do you think the seafoam thing might be an advantage to me
    Just trying to get on the water before the hot weather goes away

  5. #5
    Join Date
    Sep 2010
    Posts
    20,476

    Default Re: low compression

    What motor do you have ????----model # or serial number might help !

  6. #6
    Join Date
    May 2013
    Location
    TX.
    Posts
    490

    Default Re: low compression

    Quote Originally Posted by ko4nrbs View Post
    Go to Walmart and buy some Seafoam in the automotive section. Squirt a few ounces in each cylinder or more and let it sit for a couple of hours or so. Recheck compression. You may have to repeat a few times.

    The rings are probably stuck form sitting so long.

    When you get it running mix Seafoam with your fuel/oil mixture for a tank or two to clean the motor out good.
    Bill
    Better yet on the initial fix, google "decarb". Do that for a quicker result and "then" keep SF in your gas. Decarb is a proven process attested to by some of the biggest guns to ever post on this forum!

  7. #7

    Default Re: low compression

    89. 90 horse Johnson vro. I also have a little oil seeping from the upper part of the engine from somewhere that runs down the side of the lower end

  8. #8
    Join Date
    May 2013
    Location
    TX.
    Posts
    490

    Default Re: low compression

    Quote Originally Posted by Willie23 View Post
    89. 90 horse Johnson vro. I also have a little oil seeping from the upper part of the engine from somewhere that runs down the side of the lower end
    If I understand you, you have a little oil coming from the midsection or lower unit. 2 stroke engines burn oil with their gas. Oily residue becomes part of the exhaust along with the exhausted engine cooling water, both dumping into the mid section and running down to the drain holes and prop exhaust. If it's a small amount and seems to include water droplets, that's normal drainage for a 2 stroker.

  9. #9
    Join Date
    May 2015
    Posts
    2,360

    Default Re: low compression

    Start your own thread instead of posting on a 10 yr old one. The title is for a mercury 85 hp and your motor is a Johnson 90 you are not even in the right forum

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