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  1. #1

    Default "I have a 40 HP Mercury lighte

    "I have a 40 HP Mercury lightening XR outboard and it is a rebadged Tohatsu. The Tohatsu 40 and 50 hp are the same motor with different jetting, inlet manifold and throttle cam.

    The 40 hp lightening xr has the 50 hp jetting and throttle cam. Though the inlet manifold restrictes the intake to half the size of the carby throat.
    Is it just a matter of fitting a Tohatsu 50 hp inlet manifold to increase the HP? Or is it possible to cut/grind the inlet manifold restriction plate area to acheive the same result? If so to what size?

    This will obviously be done after the warranty period expires."

  2. #2
    Join Date
    Sep 2003
    New Tripoli, PA, USA!

    Default "Obviously! Most manufacturers

    "Obviously! Most manufacturers make their larger hp motors less so by restrictions (instead of visa-versa). I'll bet grinding the intake out would not be hard to do, but other restrictions might be lurking in there as well, like the exhaust tuner: it could be tighter.


  3. #3
    Join Date
    Nov 2005
    , il,

    Default Graham has had some good write

    Graham has had some good write ups on these mods. It goes something like when you take a xx motor and turn it into an xxx motor you acheive a 2% gain. That gain at WOT will net you 1-2 m/h increase. Long story short is its just not worth the time and effort or taking a chance of messing a perfectly good engine up.

  4. #4

    Default "found out that it was losing

    "found out that it was losing power at WOT. Butterflies were going past horizontal and the timing was incorrect. The boat would do 29mph with the tide and wind but drop down to 25mph against the tide and wind. Once the throttle linkage and timing was fixed the speed increased to 31mph with tide and wind, 29.8 mph against the tide and wind.

    I originally was not impressed by the performance of my new outboard, hence why I asked the question. Now that it is performing as it should, there is no reason to modify the engine.

    Thanks for you input."

  5. #5
    Join Date
    Feb 2009
    perth, wa, Australia

    Default Change the manifold or mod it

    Change the manifold or mod it will you notice an inprovement in accelleration and speed...it isnt going to cost anything and you dont often get something for nothing

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