Excess oil buildup 25 merc 2 stroke

Discussion in 'Outboard Maintenance' started by PG350, Apr 6, 2014.

  1. PG350

    PG350 I Love microskiff.com!

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    I have a 1997 25hp, Mercury, 2 stroke that I purchases used and was in need of several items to make it whole.  I now have the motor running and it runs very strong.  The person who had it before me had the idle set very high and it seemed to be running very rich.  I set the fuel ratio per the factory setting and it would stall when put into gear and when throttle was given.  I screwed the the fuel mixture screw out one turn and the motor seems to run great. 

    The motor does run rough at low RPM's but smooths out at little over 1/4 throttle.   

    I have ran the motor two times now with mostly slow speed running.  When the motor sits after use there is a very large puddle of dark black oil on the ground.  I am used to seeing this but no where near this much. 

    Question?  Could dirty carb be to blame and I am running it too rich to compensate?   

    Question?  What fuel mixture are you running on same motor?  I am running 50:1 but was wondering if anyone else uses different for this motor????

    I am very happy with the power the motor is producing and as it is set right now it starts easy, and runs like bat out of hell.  Just little rough at low speed before the power band. 

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  2. Brett

    Brett > PRO STAFF <

    Old tech 2 strokes are very inefficient at low rpms.
    Up to 40% of the fuel oil mix is blown out the exhaust port
    and coats the interior of the midsection. Then it leaks
    down and drips out the exhaust opening in the lower unit.
     

  3. cutrunner

    cutrunner Cert. Yamaha technician

    Everything Brett said
    But, that puddle is a little more excessive than normal unless you are doing A lot of idling.
    to me it sounds like a professional carb rebuild and adjustment is needed as well as new plugs and possibly a fuel pump rebuild for safe measure. Gaskets are cheap
     
  4. cutrunner

    cutrunner Cert. Yamaha technician

    Also make sure you are remixing your oil to the proper ratio
     
  5. PG350

    PG350 I Love microskiff.com!

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    Thank You both.

    Right before I shut the boat down I had to go through an idle speed only canal for about 30min. I also fluched the motor for another 3 to 5 minutes at idle. I am sure that was part of the problem but I will do what you suggested when I get the time and or money.