hi performance mods on 25hp

Discussion in 'Outboard Maintenance' started by HighSide25, Jan 26, 2009.

  1. HighSide25

    HighSide25 Well-Known Member

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    anyone run the special reeds in a merc? whered ya get them and how was the install?

    any other things that could be done to get a couple more ponies out of a 2 stroke?

    thanks
     
  2. B.Lee

    B.Lee Well-Known Member

    More air, more fuel, higher compression are the biggies when it comes to most any engine, especially 2 strokes. Short of increasing the displacement, these are usually the easiest.

    Reeds (I think Boyeson makes some) probably won't give you any more power, but would probably help throttle response some.

    More fuel comes from larger main jets. More air comes from larger carb inside diameter. More compression comes from shaving the head or cylinder. You can also vary port timing to change when and where the air/fuel mix is delivered, but that is far beyond the scope of this forum.

    They easiest and most effective way to get some more holeshot or top end is the change the prop. Forget engine mods unless you have the prop dialed in, you'd be throwing money away.
     

  3. HighSide25

    HighSide25 Well-Known Member

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    prop is dialed in. 4 blade powertech....
    would a 30hp merc carb fit in a 25 powerhead.
    also, how could you get a bigger main jet?
     
  4. Gramps

    Gramps Living & Dying in 3/4 Time

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    Just punch it .30 or .50 over, shave the head, port & polish, add Boysen reeds & spacers (can't remember if they need them or not) use a 30hp carb or just switch the main jet.

    When it runs it will haul ass but you'll learn how to spin a wrench reeeeel quick or no fishin.
     
  5. TomFL

    TomFL Well-Known Member

    Did Merc ever make a 30 based on the same block?

    Just curious 'cause if they did you could just compare parts lists for both and come up with the different parts needed for the 30.

    Just a thought...

    -T
     
  6. Brett

    Brett > PRO STAFF <

    and after spending all that cash, you'd find it would of been faster
    and easier to sell the motor you have, and buy a bigger motor,
    designed to deal with the higher loads and rpms.

    do a search on google for "Frankenmercs" if you want a grin.
     
  7. Jacbo

    Jacbo Well-Known Member

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    I don't think mercury ever made a 30hp two stroke. They sell 30 two strokes outside the US but i believe these are rebadged tohatsus.

    I agree with Brett and think your best bet is to look for an older two stroke yammy or tohatsu 50 under 150 lbs..... unless your talking about a highsider, in that case I'd stick with the 25!
     
  8. HighSide25

    HighSide25 Well-Known Member

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    im sticking with the merc 25. best motor ever built and i picked it up with about 10 hours on it. its the perfect weight for a gnu classic.

    the only reason i want more out of her is because i like to run at least 20 miles on a fishing trip and if i bring another person, it slows down a little and becomes less fun and more like a long boat ride. i think im going to try the reeds, they are less than 50$ and the website says you can do them yourself fairy easily. supposed to save a little on fuel as well. i guess if i get that the next step will be to add some more cup to the prop
     
  9. Gramps

    Gramps Living &amp; Dying in 3/4 Time

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    In a properly setup classic with a normal load you should be right at 30mph at WFO with two folks. Any faster than that and it gets funkin scary & fast. What are you running now?
     
  10. HighSide25

    HighSide25 Well-Known Member

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    im at like 26, its the dang 4 blade
     
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