Merc 25hp will not run at max rpms !

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

  1. RetroJim

    RetroJim I Love!

    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 .


  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

    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

    shoulda took it back!!
  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!

    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...

    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

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