Merc 25hp will not run at max rpms !

Discussion in 'Outboard Maintenance' started by RetroJim, Jul 19, 2012.

  1. RetroJim

    RetroJim I Love microskiff.com!

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    I have a 2004 Merc 25hp , 2-stroke . My problem has been with this engine since I bought it new . It will start fine , idle fine and run 1/2 throttle fine and that it !  The rpms will not go any higher than about 50% . The throttle is open wide , carb throttle is also open all the way , carb was just  rebuilt , new pump bulb for fuel tank , cleaned the carb filter & fuel tank filter . New spark plugs installed . Fuel tank connections are all good and tight . Coils are fine as well .
    I only used this engine maybe 15 gallons over the last 6 years . I bought it new and didn't run really well to me at that time . Just figured it needed time to break in .
    I did use new 2 stroke oil in the fuel along with Sta-bil Marine .
    The one and only time it ran full rpms was last month for about 1 mins then started dying at full throttle . Then I would take out of gear and it would start right back up no problem . This went on for about 20 mins or so untill it got to the point of not starting at all .
    After a crb rebuild it seemed to run ok but only at about 50% of the rpms it should be running at full throttle .
    Right now it will start and run just fine BUT will only rear 50% of the rpms the engine has .
    I am starting to wonder if the "reeds" were bad from the beginning . That is the only thing I can think that might be causing this problem .

    PLEASE HELP !

    Jim
     
  2. Brett

    Brett > PRO STAFF <

    I had an outboard that no matter what I did, it wouldn't produce full rpms.
    I knew compression was good, spark was good, fuel pump was good, intake vacuum was good,
    I finally just replaced the entire carburetor with a new one, solved my problem.
     

  3. cutrunner

    cutrunner Cert. Yamaha technician

    Turn the primestart off!! Lol just kidding
     
  4. DuckNut

    DuckNut Brandon, FL

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    Do as Brett said or try to find someone who has a set of carb jet bits and have them clean and check the jets.
     
  5. anytide

    anytide Administrator Staff Member

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    shoulda took it back!!
    -a
     
  6. Sheremeta

    Sheremeta Well-Known Member

    did you check compression? You could try to spray mercury tuner or seafoam deep creep in the jets.
     
  7. AfterHours2

    AfterHours2 Stripper in my own Mind!

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    Had the same issue on a Yamaha. Replaced endless parts. Do as Brett said and just buy a new carb. That's the problem altogether...
     
  8. Rediculous

    Rediculous Boozle on...

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    I have the same exact engine, that had the same problem. I replaced the pick up tube in the tank and all the fuel lines and bulb, cleaned the carb a little and she has ran perfect ever since. I didn't have to buy a new carb, maybe you don't either.
     
  9. islander1225

    islander1225 Well-Known Member

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    I'll give ya 500 bucks for it and then you have no more headaches lol.




    Alex
     
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