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1968 Mercury 500 questions

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  • 1968 Mercury 500 questions

    Good Morning
    I a looking for the correct spark plug for a 1968 Mercury 500 outboard with thunderbolt ignition.

    Also looking for a prop for the same model. Don't know much about props as far as pitch and diameter so am looking for some advice here.
    Thank you for the help
    Nick

  • #2
    You don't have a lot of choices for props. All are 10 3/4" and 10 - 15" pitch and 11 splines. Only Propco has new props and they've easy to deal with. Otherwise it's CL or Ebay for used.

    I think a '68 500 takes a Champion L4J side electrode or AC V40FFM surface gag. A motor serial number is needed because of design changes and which ignition system is used.
    BOAT SPECS FORUM HELP STARCRAFT FORUM SHOP iboats
    Please, no PM's (Private Messages) regarding boat/engine problems.
    That is what the forums are for.
    Only forum/moderator issues will be answered in PM's.

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    • #3
      Serial number is 2408947

      Comment


      • #4
        This Merc 500 should have the Lightning Energizer ignition and takes the surface gap plugs AC V40FFM or equivalent.

        What plugs are in it now?
        BOAT SPECS FORUM HELP STARCRAFT FORUM SHOP iboats
        Please, no PM's (Private Messages) regarding boat/engine problems.
        That is what the forums are for.
        Only forum/moderator issues will be answered in PM's.

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        • #5
          Not sure other than i know they are an NGK. Will have to check tonight for the exact number. The previous owner put the current plugs in and i want to make sure i replace them with the correct ones. I have found that some of the work done on the boat and motor was rigged up. So again just double checking to make sure i replace parts with the correct ones. The motors runs well know but tops out at around 4000 RPM. i will start with replacing the plugs and making sure the throttle linkage is adjusted correctly. The timing is not something i have much experience with but an mechanically inclined and do have a manual so i can check that also.

          Will need to replace the lower unit seals because it does leak a small amount of oil from the area between the housing and the prop. I assume that is the seal on the carrier.

          GA Boater thank you for your help here i appreciate it and will reply with more questions i am sure.

          Thank you Nick

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          • #6
            A compression test is the first thing to do.----A new water pump impeller before the next trip too.

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            • #7
              Compression is good at 130-135 per cylinder. Impellar is new with new gaskets as well.

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              • #8
                NGK replacements fo the AC plug;


                Some of those numbers are actually duplicates. For example a BUHW is a 2622. 2622 is a universal stock number used by auto parts stores.
                BOAT SPECS FORUM HELP STARCRAFT FORUM SHOP iboats
                Please, no PM's (Private Messages) regarding boat/engine problems.
                That is what the forums are for.
                Only forum/moderator issues will be answered in PM's.

                Comment


                • #9
                  Ok i replaced the plugs and still only can get it to 4200 rpm at WOT. tops out at 21 mph with myself fuel and battery on board. Could it be that the throttle linkage needs adjusted?
                  Would advancing the timing have any effect, i am kinda lost on this one.

                  Last night i did notice the prop shaft has a very very slight bend to it you can see it when you spin the prop by hand.

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                  • #10
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                    Don't mess with the timing. It's set at the factory and will stay in time forever unless it's messed with.

                    A bent prop shaft isn't helping.

                    Push the throttle full forward and check that the carb butterflies are completely open.
                    BOAT SPECS FORUM HELP STARCRAFT FORUM SHOP iboats
                    Please, no PM's (Private Messages) regarding boat/engine problems.
                    That is what the forums are for.
                    Only forum/moderator issues will be answered in PM's.

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