Logo
Get instant online access to repair manuals for your Mercury / Mariner outboard. Online Manuals
MercuryMariner
Order printed Mercury / Mariner service manuals — shipped to your door! Printed Manuals
MercuryMariner
Use engine diagrams to find & order parts for your Mercury / Mariner engine. Engine Diagrams
MercuryMariner
Find parts quickly with Mercury application guides. Quick Parts Guide
MercurySierraCDI
Results 1 to 5 of 5
  1. #1

    Default '99 25HP conversion to 30HP??

    1999 Tracker Marine 25HP 2-stroke.

    I've read that some 2-stroke 25HP's can be easily converted to 30HP. Does anyone know if mine can be converted? If so, any links to instructions would be much appreciated!!

    thanks!

  2. #2
    Join Date
    May 2007
    Location
    Inverary, Ontario, Canada - The Great White North Eh!
    Posts
    9,114

    Default Re: '99 25HP conversion to 30HP??

    Not sure where you heard that.

    The 25 shared a powerhead with the 20 horse (about 25 cubic inches of displacement), not the 30 (39.4 cubic inches of displacement which was shared with the twin cylinder 40 horse). So you can "detune" yours a bit but can't bump it up enough that you will notice.

    In small outboards the max horses is pretty well limited to the displacement (on a 1:1 basis), and the 25 is already at the max.

    On models that can be converted 9.9 to 15, 20 to 25, 30 to 40 etc, the cost is usually significant. It can encompass changing the carb or reed valves/plates, altering or changing the exhaust plate/tube etc (big bucks compared to the price of the motor).

    AND, if you live in the U.S. it is illegal to alter the horsepower of the motor (unless you have a racing exemption - thank the EPA for that law). Ok, that wouldn't stop alot of guys, but should an accident ever occur and things were investigated you can be sure that the fact the motor was illegally altered would weigh heavy on determining fault (so something to consider for US residents).
    Graham

    A "professional" is someone who gets paid for their work - it doesn't necessarily mean they are good at it :)

  3. #3
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    15,200

    Default Re: '99 25HP conversion to 30HP??

    ..."...if you live in the U.S. it is illegal to alter the horsepower of the motor "

    If that's the case, I believe that's only on newer motors.

    Jeff

  4. #4
    Join Date
    May 2007
    Location
    Inverary, Ontario, Canada - The Great White North Eh!
    Posts
    9,114

    Default Re: '99 25HP conversion to 30HP??

    Here's the good word from Merc -

    EPA regulations prohibit changes to engines that could affect emissions limits. Per the service manual, "The dealer and/or consumer is not to modify the engine in any manner that would alter the horsepower or allow emission levels to exceed their predetermined factory specifications." The only changes permitted are carburetor jet and gearcase/gear ratio changes for high altitude operation as detailed in applicable Mercury Marine Service Manuals.

    The EPA regs that they reference came into effect in August of 1996 - so yes Jeff, like you I have old motors (newest is a 1991) and it doesn't apply to us (or me in particular living north of the border), but in this case, if this 99 model resides in the US it legally can't be modified (and will have an EPA sticker on it somewhere to show compliance).
    Graham

    A "professional" is someone who gets paid for their work - it doesn't necessarily mean they are good at it :)

  5. #5
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    15,200

    Default Re: '99 25HP conversion to 30HP??

    A 1991? That's a NEW Merc to me, brother!

    Jeff

Similar Threads

  1. Difference between 1995 Evinrude 25HP and 30HP
    By drbridge in forum Johnson Evinrude Outboard Forum
    Replies: 5
    Last Post: 06-12-2012, 09:29 AM
  2. 1993 25hp Lower unit swap 1988 30hp
    By mdbasser in forum Johnson Evinrude Outboard Forum
    Replies: 1
    Last Post: 07-02-2010, 02:46 PM
  3. Johnson 25ho to 30hp conversion
    By wh500special in forum Johnson Evinrude Outboard Archive
    Replies: 2
    Last Post: 11-07-2006, 08:49 AM
  4. 25hp to 30hp Johnson
    By don in forum Johnson Evinrude Outboard Archive
    Replies: 1
    Last Post: 09-15-2003, 03:05 PM
  5. Power Conversion for b90 25hp Johnson
    By Charlie M. in forum Outboard motors archive 2000-2004
    Replies: 8
    Last Post: 02-27-2003, 10:04 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •