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Correct Spark Plug for 1974 Merc. 7.5 hp

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  • Correct Spark Plug for 1974 Merc. 7.5 hp

    Last week I had put up a post about my Merc. 7.5 hp having troubles starting. The motor runs great when I get it going, but have a hell of a time getting the thing started. The only way I can get it started is by tilting the motor out of the water and pulling it about 15 times or to put wd-40 in the cylinders. I've done a little research and believe I've been using the wrong spark plugs. I've been using a champion L78v plug when I think I should be using a Champion L77v plug. Does anyone know the difference in these two plugs? Could this be my starting Problem? The l78v is a no gap plug. Any help would be appreciated.

  • #2
    Re: Correct Spark Plug for 1974 Merc. 7.5 hp

    Bosch BR9HS-10,Champ L77V.But I think your problem will be carb ot fuel pump related,given what u said about the WD40 and tilting ritual before it starts.
    "Did you hear about the guy whose whole left side was cut off? He's all
    right now."


    • #3
      Re: Correct Spark Plug for 1974 Merc. 7.5 hp

      Hi,If you get it going, it will run the best with Champ L77J4C gapped at .040....have fun...corm
      This is free internet advice.

      Have Fun,


      • #4
        Re: Correct Spark Plug for 1974 Merc. 7.5 hp

        Thanks alot for you advise. I'll give it a try. I should have mentioned that I've replaced the fuel pump diaphragm and gaskets, also the needle seat and checked all the jets in the carb. I've also replaced the primer bulb and fuel lines and checked the fuel line filter. I've been working on this problem on and off for the last 3 yrs. Even had it in two different shops and they counldn't find the problem.I don't think they tried real hard though. I was messing around with it today and it seems like the bottom cylinder isn't getting the gas like the top cylinder is. Both cylinders are working when its running, because I pulled one plug wire off at a time and it keeps running on one cylinder. Not sure what to try next. Any more advise would be apprecaited