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Idle adjust on merc 115HP in line 6

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  • Idle adjust on merc 115HP in line 6

    Can someone tell me how to adjust the idle mixture on this engine?
    I have cleaned all carbs, new fuel lines, etc.
    My engine runs great except after I idle for a couple minutes, then when I go to WOT it bogs down until it gets some rpm's then it runs fine.

  • #2
    Re: Idle adjust on merc 115HP in line 6

    First make sure the fuel pump is not leaking raw fuel into the crankcase.

    Normally when you set the carbs, you start out at 1-1/2 turns out from lightly seated. You then adjust for smooth idle. Then you test for acceleration. Usually the motor will fall on it's "face" and you will likely need to richen the mixtures, top carb first, then mid carb and finally bottom carb, testing acceleration after each adjustment. Open each carb 1/8 turn and test to see if acceleration improves. Repeat until you have maximized acceleration and have reasonable idle quality. It is important to use fresh mixed 50::1 fuel

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    • #3
      Re: Idle adjust on merc 115HP in line 6

      How could I check to see if the fuel pump is leaking into the crankcase

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      • #4
        Re: Idle adjust on merc 115HP in line 6

        You have the single figure 8-shaped fuel pump, right? The fuel pump will have two pulse lines on it's bottom. Remove them from the pump and then pump the primer. If you see fuel drip from the pump, the diaghram is bad, and you need to rebuild the fuel pump.

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        • #5
          Re: Idle adjust on merc 115HP in line 6

          My fuel pump is square

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          • #6
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            Re: Idle adjust on merc 115HP in line 6

            I adjusted the carbs and it runs great. Now I need to pull a skier for the real test

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