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1981 mercury 175 hp power loss

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  • 1981 mercury 175 hp power loss

    I am new to the outboard world but have been a mechanic for 30 yrs. I am having a fit trying to get this 2 stroke thing. I have a Mercury 175 hp that was running fine and it just lost power. It idles fine but don't dare give it gas. I have changed the stator, both switch boxes, rectifier, all three carbs, fuel pump, new fuel tank and hoses and fuel filter. I have 115 psi compression across the board. I ran it without the air box and noticed that while I applied the throttle the fuel would start spitting out the carbs. if I tilt the motor upward it would pick up some rpm's. It idles good, It loads up on fuel as I accellerate. So any help would be appreciated. Oh and I have tried new spark plugs also.


  • #2
    Re: 1981 mercury 175 hp power loss

    When you changed the stator, is it posible you damaged/sheared the flywheel key? Fuel spitting out the carbs leads me to believe you have the carbs out of whack, might want to go through them again. Why did you change the switchboxes and the stator? Did you check for spark? Do you have good spark? Spark pluggs can be bad right out of the box, as you probably already know. Throw some new pluggs at it, as 2-strokers eat pluggs and read the old pluggs and let us know what you find

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    • #3
      Re: 1981 mercury 175 hp power loss

      Like he said, basic things. It has compression, so that's good. It idles fairly well, so the reeds are usable. Does it have strong spark on all 6? How about the linkage and ignition timing. (link-n-sync procedure).

      The formal link-n-sync procedure will usually uncover basic problems. If something doesn't drop in where it should, you can usually figure out what's causing it. For instance if it won't idle with the carb butterfly's shut, there's trouble in the idle circuits.

      If I had to guess, your problem is something basic is wrong with all the carbs, (mechanic's error) or the linkage isn't progressing properly, or the timing is off.

      These 2 poppers are pretty simple compared to a modern 4 stroke.

      hope it helps
      John

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      • #4
        Re: 1981 mercury 175 hp power loss

        The biggest difference between outboards and the ring-ding dirt bikes of old is the reed valves in the intake, which prevent the backflow of air thru the carb as the piston comes down, pressurizing the crankcase.

        If a reed valve fails then crankcase air can spit out the carb, this air movement also re-carburates, adding more fuel, and on the inflow again adds even MORE fuel, flooding the cyl and killing the plug.

        Inspect the reed valves for any cracks, splits, or chips. Hold them up to the light to look for a good seal, a slight gap about the thickness of a sheet of paper (.003) is all that is allowed as crankcase pressure should close that completely.

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        • #5
          Re: 1981 mercury 175 hp power loss

          John's right, if it idles fine then the reeds are probably fine.

          The other great difference between the 4 stroke that you are used to and this 2 stroke, is the lack of an accelerator pump or enrichener for fattening the fuel mixture as the throttle opens.

          The 2 stoke idle mixture is set fatter than best idle, like the 4 stroke.

          Reset the idle to best idle IN GEAR while on the water, then further richen the mixture almost 1/8 turn.

          Any lean miss, hesitation or throttle bog shows a need for more idle fuel mixture.

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          • #6
            Re: 1981 mercury 175 hp power loss

            the carbs have no idle air adjustment they are replaceable jets so would I go up or down to fatten the fuel? I am going to set the link and sync and ensure that it is timed corectly. The flywheel don't use a key it has the double spline. I was told by a local marine shop that they were sure that it was the stator. As fore the switch boxes ignorance is all I can say about that. Or maybe it is the sign of a desperate man LOL. I will check the reed valves I have the repair manual and it gives you the gaps. Thanks for the advice I will let you all know what I find out. I will put in a fresh set of plugs. I have two sets of carbs and they both do the same thing. Good idle no power. one time it actually got on plane and ran okay so maybe the timing is the answer. Got my fingers crossed.

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            • #7
              Re: 1981 mercury 175 hp power loss

              That stator has two sets of ignition windings, low speed and high speed.

              Low output on a high speed winding will idle fine, and even run up NO LOAD RPM, but bog under load.

              Download the free Ignition Troubleshooting Guide from CDI found thru the links at www.rapair.com

              Find your model then follow the steps to test.

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