1996 Mercury 90HP ELPTO Bogging Down at WOT

Discussion in 'Outboards' started by Richard Mac, Sep 13, 2018 at 4:01 PM.

  1. Richard Mac
    Joined: Thursday
    Posts: 3
    Likes: 0, Points: 1
    Location: Alberta

    Richard Mac New Member

    Hi All: First post here. I'm a dedicated do-it-yourselfer but am at a loss. I have a 1996 90 HP mercury elpto that's giving problems. This boat has some issues when power is added. It hesitates and then stays at low rpm's.

    To date I've confirmed fresh fuel with no H20 in it, put new gaskets in the fuel pump, changed an ignition coil and changes the spark plug wires.

    Oddly enough, changing out the wires did "fix" the issue for about 45 minutes and then the issue came back.

    I tested the coils according to the SELOC manual and #3 looked like it could be bad. Changed that out but no joy.

    Pulling the plugs after running it showed a clean plug in top cylinder so I was also suspecting water getting into the cylinders. I tightened up the bolts on the exhaust manifold cover - they all moved about 1/4 to 1/2 turn.

    I did a carb rebuild last season when it was running rough but it turned out that I had water in the gas tank.

    The trim tilt is also not working properly (it slowly comes down from tilt position). I've added oil to the cylinder but can't see how this is related.

    I'm thinking that it could be a plugged jet in the carb, water getting into a cylinder or some other ignition related issue.

    All advice appreciated!
     
  2. Mr Efficiency
    Joined: Oct 2010
    Posts: 6,661
    Likes: 166, Points: 63, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Welcome, you are a little unusual amongst outboard motor troubles posters, in having and using a workshop manual ! Certainly, running checks according to what is laid out in the troubleshooting procedures, is a big advance on guessing and replacing parts on a whim, etc. Have you run through testing all ignition components ? Replaced the plugs ( usually a good idea, as it isn't that expensive) ? You might even do a compression check ( follow manual's instructions with that) while looking at the engine, if there is a problem with that, the other stuff might not be worth spending big bucks on.
     
  3. Richard Mac
    Joined: Thursday
    Posts: 3
    Likes: 0, Points: 1
    Location: Alberta

    Richard Mac New Member


    Thanks for the quick reply! I did the plugs earlier on. Compression test may be next then.
     
  4. Mr Efficiency
    Joined: Oct 2010
    Posts: 6,661
    Likes: 166, Points: 63, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    All sorts of things go wrong with old outboards, but that one plug has a different appearance to the others, does seem a clue.
     
  5. Richard Mac
    Joined: Thursday
    Posts: 3
    Likes: 0, Points: 1
    Location: Alberta

    Richard Mac New Member

    Other threads point to either coils or water in the cylinder steam cleaning the plug
     

  6. Mr Efficiency
    Joined: Oct 2010
    Posts: 6,661
    Likes: 166, Points: 63, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Water in the cylinder has to be a serious concern, I am assuming you are in fresh water, but in salt, it would be a case of a immediate pull down of the engine, rust will kill the motor in short order. Water can also enter via exhaust plates becoming perforated. But Mercury seems to have had better metal than most, since they changed alloys in the 80's.
     
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