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Merc 50hp Only Firing On 2 Cylinders

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  • Merc 50hp Only Firing On 2 Cylinders

    Hi There
    I Have Recently Bought A Shetland With A 50 Hp Mercury 3 Cylinder. The Engine Starts And Runs Ok But When Put Into Gear The Engine Slowly Dies. Upon Furthere Inspection It Is Only Running On The Bottom 2 Cylinders Loads Of Compresssion Loads Of Spark But Not Running On Top Cylinder. Any Suggestion As To The Set Up With The Carbs, Firing Order Ect Ect Bottom 2 Are Burning Nice And Blue But Only Lite Amount Of Fire In Top Cylinder. Suspect Fuel?????
    And Help Would Be Most Appreciated
    Regards Simon

  • #2
    Re: Merc 50hp Only Firing On 2 Cylinders

    It sounds lean try richening the idle screw on the top carb 1/4 turn and see if that helps about the only other possibility for what you describe would be a bad reed and you don't want to go there.


    • #3
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      Re: Merc 50hp Only Firing On 2 Cylinders

      Have your patner try squeezing the primer bulb, a weak fuel pump will not fill the top carbs and run out of fuel under load.

      If the primer bulb greatly improves it then plan on rebuilding or replacing the fuel pump.