Yamaha 25 HP mod

Discussion in 'Outboard Maintenance' started by Frank_Sebastian, Aug 1, 2009.

  1. Frank_Sebastian

    Frank_Sebastian Well-Known Member

    Hi everyone,

    I wanted to mention a small mod that seems to have fixed a very stubborn problem with a 2005 25 HP 4 stroke Yamaha. Several people had worked on the carb including the dealer that sold it. It never ran well for more than a few weeks whenever the carb was done. Eventually a new carb was purchased and installed. No better results were had and it was done several more times over the course of 4 years.

    In march a man who lives in Sebastian tried boring out the high speed jet by 3.5/1,000. Since that time the engine has been used several times a week and almost daily this summer with no more problems. I wouldn't recommend this to others unless you have had ongoing problems with a carburetored engine.

    Best regards,Frank_S
  2. DblHaul

    DblHaul SW Florida

    What was the problem, not starting?
    (Glad to hear it's fixed!)

  3. Frank_Sebastian

    Frank_Sebastian Well-Known Member

    Hi DH,

    The engine would surge during acceleration and did not have a top end near what it should, even with a very light skiff to push. The first few times after a carb cleaning it would do better, but was never right. It now continues to run "near normal", but the HP curve is still on the anemic side for a 25 HP. I ran my 8 HP Tohatsu 2 stroke on the same boat (it is used to collect bait from pigfish traps) and it wasn't that far behind the 25. The engines we have had the most trouble with are small Yamaha 4 strokes. I know the problem is fuel related. I am driving to Melbourne to buy no ethanol fuel friday. Three of us are going with about 45 gallons of fuel capacity in the gas cans we have bought and borrowed.

    I suppose we are legal to haul it in a pickup with a cap on it?

    Best regards,
  4. TomFL

    TomFL Well-Known Member

    I think it's legal but I'm sure the state would like to charge you a fuel tax for each mile you're transporting it.

    The straight gas might be your ticket to happiness, Frank!

  5. Lex_Johnson

    Lex_Johnson I Love microskiff.com!

    What exactly was your engine doing? I have a 2 stroke 25hp Yamie, and it's been acting funny for awhile now. At WOT and near WOT, it will sort of bogg down a little, then pick back up. That's the best way I can describe it. It just sort of loses a little power, then catches back up again. But the motor doesn't seem as fast as my old 25hp, and this one has a SS prop and all.
    I tried the Seafoam decarb trick, and it didn't seem to help. I'm sure the carbs probably need a rebuild, just been putting it off. My mechanic told me the way to check is when the motor boggs down a little, push the choke and see how it reacts. If it catches itself and gains speed, it's the carbs starving for fuel...
  6. tom_in_orl

    tom_in_orl Founder of Microskiff, Member of the Gheenoe Army

    Well this thread is timely. My 25 HP 2 stroke Yamaha purchased in 2007 and has 162 hours on it has been a little weak lately too. I took it to Haley's marine in Edgewater who is not a Yamaha dealer but has a very good reputation. They ended up replacing the jets. When I asked about it being fuel related I was told 80% of the problems they are seeing right now are fuel related.  :mad:
  7. noeettica

    noeettica Well-Known Member

    Ah Ha [smiley=thumbsup.gif]
  8. grego

    grego Well-Known Member

    had the same thing happen on my sons skiff. It has a 06 25hp yami. If you pull the choke out 1/4 to 1/2 it should run fine but your carbs need work.