15hp mercury help needed bad

Discussion in 'Outboards' started by racing fan, Feb 12, 2011.

  1. racing fan
    Joined: Nov 2010
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    racing fan Senior Member

    i got a new 15 hp 4 stroke mercury short shaft motor 2 cylinder inline, 21.4 Ci., 351 cc, Bore and Stroke (in / mm) 2.40 x 2.36in 61 x 60mm 2 valves per cylinder, carb.,111lbs, I need to kick up the power a bit and i heard a long time ago that newer mercury motors have interchangeable parts like a 75 hp can turn into a 100 or 125hp just by changing like a carb or a restriction plate now i know that's true but is that true with the 2010 15 hp 4stroke (regular not pro kicker) an I looked at the 20 hp model every things the same but diff carb or a restrictor plate now could i squeeze 25 hp out of it or is 20 the max on this one and if i could how could I like i know what to do with the plate but what carb do i put in
    thanks please help
     
  2. tunnels

    tunnels Previous Member

    Just go get a bigger out board !! with the extra hp on the 15 mechanics they will crap out quicker and bit start to break , Bigger is better got for broke !!:p
     
  3. racing fan
    Joined: Nov 2010
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    racing fan Senior Member

    well i could but from what i can tell the motor could take it but it is mercury lets go cheap and sell motors for more i think
     
  4. Frosty

    Frosty Previous Member

    Some engines are detuned to satisfy the customers requirements. This is something you should have looked at before you bought it by comparing HP and bore x stroke on the brochure.

    There is no books or information on this kind of thing, infact you not supposed to know about it.

    A mechanic would pull it down and look for restrictions etc but if there isnt any then you would definitely be better off buying a bigger engine

    carbs 111 lbs?????? I think you should leave it alone --at least till your warranty is out.
     
  5. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    The 15 HP, the 15 HP pro kicker and the 20 HP Mercury outboards are all the same. Yes, you can up grade the 15 to a short shaft 20, but it depends on the model 15 you have. There's a few different ones and the easiest way to sort things out is to download their parts catalog for each engine and cross reference part numbers, like the carburetors or idle jets or main jets, etc. This is where you will find the differences.
     
  6. Frosty

    Frosty Previous Member

    There was a very simple 15 minute conversion from the Evenrude /Johnson 2.5 to the 3 HP.

    This maybe what you are referring to when you say restriction. There was a restriction plate inside the carb that could be simply plucked out. The 85 Evenrudes could be easily changes up to 115 with big bore carb changes, but these day are over.

    The little 2.5 now have a long slide that can not open fully, this needs the slide to be cut off to open, needing much more care and knowledge.

    It may be possible to upgrade your 15 but there is no written information on it.

    Where did the long shaft short shaft conversion question come from
     
  7. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Except on the very small engines, that happen to share block families, HP upgrades are usually much more involved then just a throttle limiter or restriction plate. Most times, you'll need timing and carburetor changes, if not gear sets and other major component swap outs.

    It's foolish to think that a simple orifice plate is all the difference, again except on the very small engines, which also usually have the same adjustments necessary (timing, metering jets, etc.)
     
  8. Frosty

    Frosty Previous Member

    Its not a case of tuning up but more of removing the tuning down.

    However the 15 HP 4 stroke I hav'nt a clue
     
  9. racing fan
    Joined: Nov 2010
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    racing fan Senior Member

    i looked more at the parts there is a restricor plate in the carb. and if i pull that out i will get to 20 hp or close but i may half to play around with the jets but the reeds, valves, rods, crank case parts are all the same as the pro kicker and the 20 hp model of the last 2 years 09-10 and 10-11. So i think i could pull it off any more help would be nice thanks i know i shouldn't know this mercury makes millions because not many know this info but i know some people that mess with mercs for fun and a job no names though
    note i have the 2010 regular stock 15 hp 4 stroke short shaft with a new quicksilver racing lower on it i put on but same gear ratio just lighter and better parts this motor if on dyno would be 13 full blown hp just like in the 70's but yes every thing is detuned i think 6-8hp
     
  10. racing fan
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    racing fan Senior Member

    any more help??????
     
  11. vtangler
    Joined: Jun 2011
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    vtangler New Member

    Did you ever find out necessary parts, etc?
     
  12. pistnbroke
    Joined: Jan 2009
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    pistnbroke I try

    this post goes back 8 years I think its dead
     
  13. racing fan
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    racing fan Senior Member

    actually i found some it had a really restrictive (restrictor plate) and it had a different carb i think i haven't looked into it much yet I am still working on it but for the boat i got a 1960 mercury 300 4 cylinder inline 35hp thunderbolt short shaft
     
  14. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    All the racing tricks work on these engines: remove all casting flash, do a perfect port match and polish, full seating rings, relieve the hard bends in the air/fuel path on both sides of the combustion chamber, etc., etc., etc. I have a 20 HP that pulls an honest 30 HP, by removing restrictions (intake and exhaust), cleaning, polishing, deburing, radiusing, increased timing and larger high speed jets, the usual stuff.
     

  15. racing fan
    Joined: Nov 2010
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    racing fan Senior Member

    k man i will look into that
     
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