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Classic 50 Loss of Power and Reduced RPM

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  • Classic 50 Loss of Power and Reduced RPM

    Xposted on marineengine dot com

    Motor Info:

    Serial No: A999862
    4 cyl.
    PARTS CATALOGS: 13287 - 45/50 Hp
    WOT: 5000 - 5500
    Mixture: 50:1
    Gear ratio: 1.83
    • 13 splines
    • 10 5/8 diameter by 12" pitch Black Max prop?
    Gear Oil - 80, 90, or 80w-90 GL-5


    Motor ran fine last few uses. On my previous trip, from the launch, she was slow to get up, and was running slightly rough at WOT. WOT decreased by maybe 500 RPM during the trip out. Spent the night out.

    On the return trip, she was even slower to get up. WOT decreased significantly to about 2000 RPM and even that 2000 RPM didn't seem like it would a typical full-power 2000 RPM. Running a little rough, not a consistent miss, but an occasional one.

    Back home on muffs, started fine, idles fine. Still slightly rough when the RPMs are raised on muffs. Stated doing something new... would idle fine for a while, then RMPs would jump from around 1k to around 2k. Seafoam additive in fuel, Seafoam carb cleaner in carbs. Started and idled slightly better, but not significant change besides that.

    Noticed water coming out of the engine through a hole to the left of the top spark plug. Research indicates that it's a block cover gasket issue.

    Back in the water today. Will get to about 4000 RPM, but the power is not there. Running rough at higher RPM, but hard to call it a consistent missfire... but maybe. Idles fine.

    It doesn't seem that the the block cover gasket would allow water to get into the cylinder and cause a power loss. Plan to change, but want to get to the root of the problem as well.

    I will run a compression test, but in the meantime would like to start getting the advice below.


    1) Best plan of attack?

    2) Could it be water getting in under higher pressure (when RPMs are up) from another gasket (cylinder black to baffle or baffle to exhaust)? Could this be causing the power loss?

    3) Can someone share the correct parts diagram for this motor?