Mariner 25 problem

Discussion in 'Outboard Maintenance' started by hmsmithjr, Dec 24, 2010.

  1. hmsmithjr

    hmsmithjr I Love microskiff.com!

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    I have a new to me 25 mariner mid 90's that my father in law gave me. First off it is not in the best of shape, but I had it running great. Took it out for my first real run and it ran perfectly for about an hour then cut power by about half, wouldn't plane and ran like crap. Got home and tore into it looking for an electrical problem (felt like only one cylinder firing) and found a bad coil. The magnet and grounding strap had broken. So i replaced both coils and took it to the water today. It was much easier to start and idled pretty good, but not as good as before the power loss. Anyway as soon as I hit the throttle it started back running rough and would barely make any power. I have recently cleaned out the carb and replaced the plugs, but have done nothing with the fuel pump diaphram. I do not think it is a fuel issue, I believe it is electrical. Does anyone have any Ideas of where to help me get started.
    Thanks,
    Maclin
     
  2. hmsmithjr

    hmsmithjr I Love microskiff.com!

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    btw my compression is about 110 PSI is that about right
     

  3. levip

    levip I Love microskiff.com!

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    while running the the engine in gear and full throttle pump the fuel bulb if it picks up speed and runs better its most likely the fuel pump you can also try this while idling
     
  4. levip

    levip I Love microskiff.com!

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    yeah thats about right as long as its on both cylinders
     
  5. aflatsnut

    aflatsnut I Love microskiff.com!

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    Could be going into engine slowdown mode due to overheating, or engine oil sensor. This will exibit itself as smooth idle, easy start, and running real bad if you give it throttle. Same symptom as hitting the rev limiter at WOT.

    Bob
     
  6. anytide

    anytide Administrator Staff Member

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    i had a '98 after several years of great performance , it started doing the same thing.. if possible $$$   -replace all the electrical components. i did it to mine and it ran perfect again for many years,,
    -i think some of the parts were called :
         -trigger
         -coils
        -brain ?
       -stator
         i did this before messing with the carbs, i always ran all the gas out during the flushing process and for 12 years NEVER had a carb issue.
    -compressions sound OK----
                 good luck        -anytide
     
  7. mark_gardner

    mark_gardner I Love microskiff.com!

    i dont think this is an issure with this motor, the 2 strokes are pretty simple. sounds like a fuel issue to me, make sure you start with a clean tank, clean fresh fuel, good fuel lines preferably new :) i've had issues similar to this with 2 different merc 2 smokes and solved the problem simply by removing the carb, unscrewing a few of the little cover plates and bowl and hosing down real good with carb cleaner and now they run like a scalded dog :eek: ;D
     
  8. cutrunner

    cutrunner Cert. Yamaha technician

    Ok, heres what you do. Buy one of those 5 dollar inline spark checkers that plugs in between your sparkplug and wire, check both cylinders while the motors running and make sure both sparks look equally strong, if so its not an electrical issue. But mercury isnt best known for its "good" electrical parts ::), if its not electrical its carbureator, to me it sounds like the lowrange-idle circuit is clogged. Also check for loose or dirty grounds and connections :cool:
     
  9. Frank_Sebastian

    Frank_Sebastian Well-Known Member

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    You can do a real quick spark check with a good insulated screwdriver. Test one coil at a time. You should have a hot blue/white spark on each. We used to make our own Home made spark tester for this job, but a screwdriver shoved inside the plug wire cap will work.

    Frank_S
     
  10. hmsmithjr

    hmsmithjr I Love microskiff.com!

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    Thanks for the ideas. I have not had a chance to mess with it yet, but I will be able to work on it in the next few days. I will keep ya'll updated.
    Maclin
     
  11. hmsmithjr

    hmsmithjr I Love microskiff.com!

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    Ok. So I think I have it narrowed down to the electrical switch. I am only getting power to one of the wires out of the switch and the other one is dead. I have tracked down the part and it appears that I am looking between $110 and $160. The only issue is that my # is 339-7452a17 and the only one I can find ends in 19. Is this the new part # or is it something else. Also how will I know which of the wires going to the coils goes where. They are both green with a yellow stripe.
    Thanks,
    Mclin
     
  12. Brett

    Brett > PRO STAFF <

    Parts numbers get changed. May have happened to yours.
    Talk to your parts dealer and ask if this has occurred.
    Wires from switch box to coils are not only color coded,
    but are numbered also. Check closely.
     
  13. noeettica

    noeettica Well-Known Member

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    Here's a photo from a running Matiner ... Green with yellow stripe goes to top coil

    hope this helps ...


    [​IMG]
     
  14. hmsmithjr

    hmsmithjr I Love microskiff.com!

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    Guys,
      Thanks for all the help and input.  I replaced the electrical switch and it is running like a scalded dog above idle. However, now at idle it runs rough and does not idle low like it did before the switch went out.  I am thinking the fuel pump diaphram on the side of the carb could be the problem, but am not sure.  At idle it is shaking real bad but above that it runs great.  Any ideas?

    BTW I did a speed run with my GPS and got 30.2 MPH with just me and 3 gallons of gas.
    Maclin
     
  15. twitch

    twitch Well-Known Member

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    Sounds like a lowspeed jet is stopped up.
     
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