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Mercury will start cold, won't start hot!

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  • Mercury will start cold, won't start hot!

    I have a 2003 Mercury 115 EFI Four Stroke, which will start like a charm first thing in the morning at the boat ramp and run great to the first couple fishing destinations. But a little later in the morning after those first couple starts and stops the motor becomes progressively harder to start.
    I check to make sure the primer bulb is hard.
    It is getting sufficient power from the batteries, I charge them at home between each trip.
    I've checked and replaced fuel filter in motor and in-line water fuel separator element. Bowl on water fuel separator has had no debris or water in it.
    Checked fuel cooler water pressure for clog/debris, thinking this could be a vapor lock problem - no problem there, the water lines are clean with good flow.
    Spark plugs look ok.

    Once I do finally get it started, it runs fine at any RPM.
    Not sure what to check next.

    Anyone have any advice for someone who wants to get back out fishing, but now fears going too far from the dock?!

  • #2
    Re: Mercury will start cold, won't start hot!

    Any advice out there?

    Much appreciated.


    • #3
      Re: Mercury will start cold, won't start hot!

      Do you have a manual?if so I would be looking at troubleshooting EFI system first.Could also be a compression issue.Grab a gauge and check your compression,cold and then warmed up.
      "I hear and I forget. I see and I remember. I do and I understand."

      Haines Hunter V17C Half Cabin. Mercury V6 135 HP 1988.


      • #4
        Sign up today
        Re: Mercury will start cold, won't start hot!

        Why do you have to charge the batteries every time at home?

        Failure of the charging system to keep up with the electrical loads during operation will reduce cranking speed as the batteries get lower, making for more difficult starting.