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  1. #1
    Join Date
    Sep 2016

    Default 1987 Classic 50 Plugs wet

    Recently Purchased a 18' Lowe Jon with Mercury Classic 50, 45 HP. Sea Trial went well, and after the purchase lost #3 and #4 cylinder ignition. Ended up replacing Stator, Rectifier, and Trigger. Upon inspection they had been replaced with the wrong part numbers, thus leading to the failure. Now the charging system, ignition, is all working well.

    The carbs were rebuilt 6 months ago, prior to my purchase of the boat. It has all new fuel lines, Racor filter and separator, new filter under the cowl. Essentially a totally overhauled fuel system.

    Now I have two problems.
    1. After a solid day on the water, all ran well. The next day, it fell on its face. Pulled the plugs, dried them off, fired back up and ran all day. That night, went back out, fell on its face again, bogged, wouldnt make over 2500 rpm. Pulled the plugs again, #1 was fouled Black. #4 same. Is this a mere adjustment issue(fuel mixture) or possible a stuck needle and seat?

    2. With excellent water flow, I get an over heat alarm at 5000-5500 RPM, back off to 4800 and it clears within seconds. Faulty sensor?

    The engine was originally a durablend, but it had been removed. I'm running non-ethanol fuel and a ratio of 50:1

    Any help would be appreciated.

  2. #2

    Default Re: 1987 Classic 50 Plugs wet

    If sparks 1&4 are fouled black both carbs would have an issue.. unlikely then that 2&3 are ok.
    Probably a faulty spark, -broken cable or dirt at the spark plug plugs..
    Only 2.500 rpm could indicate a missing cylinder.
    The overheat might be real, if the engine has not been flushed well over time, and some tube has reduced diameter/water flow due to silt build-up

  3. #3
    Join Date
    Sep 2016

    Default Re: 1987 Classic 50 Plugs wet

    Thanks for the reply. It looks as if I have multiple issues and since it has been a random issue, I'm replacing the switch box and putting on new spark plug wires, who knows how old they are.

    Now on on the over heating issue, some direction as to where the clogs may be and how to clear them. I've seen some diagrams of equalization tubes an wonder if there are auxiliary bypass tubes for the cooling system.

  4. #4

    Default Re: 1987 Classic 50 Plugs wet

    I once had an 86 classic 50. I had an issue with it running on 2 cylinders although I do not remember which two. The switchbox was the problem for me. As far as the overheating, there could be pcs that broke off an old impeller lodged somewhere in the water jacket. It could be silt as well. I would imagine a passage is partially blocked and it just won't flow enough water at the highest rpm`s. Maybe someone will chime in as to tell how much access to the water jacket is possible.

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