# Mariner 25 problem



## hmsmithjr (Dec 3, 2010)

btw my compression is about 110 PSI is that about right


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## levip (Dec 4, 2010)

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


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## levip (Dec 4, 2010)

yeah thats about right as long as its on both cylinders


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## aflatsnut (Feb 12, 2010)

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


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## anytide (Jul 30, 2009)

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


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## mark_gardner (Mar 18, 2009)

> 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


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  ;D


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## cutrunner (Jun 8, 2010)

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


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## Frank_Sebastian (Oct 15, 2007)

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


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## hmsmithjr (Dec 3, 2010)

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


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## hmsmithjr (Dec 3, 2010)

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


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## Brett (Jul 16, 2008)

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.


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## noeettica (Sep 23, 2007)

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

hope this helps ...


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## hmsmithjr (Dec 3, 2010)

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


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## twitch (Mar 4, 2007)

Sounds like a lowspeed jet is stopped up.


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