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possible carb swap?

I

inthebush

New member
to those of you that know alot about motors, this might seem like a dumb question but here goes anyways.
is it possible to take a carb from a 15 hp 4 stroke and put it into a 8hp 4 stroke motor?
(they seem to be the same motor other than the 15 has a larger prop and a different carb)

thanks
 
I can't speak if the motor is "really new" (like the last couple of years - my most recent specs are 2008) but the displacement was different, by almost 140 cc's between the 8's and 15 horse models.

The small 4 stroke Merc's are built by Tohatsu so they are mechanically identical to Tohatsu's own brand and Nissan's of the same horsepower.

So while you can turn the 8 into a 9.9 by rejetting the carb (only real difference I see at a quick glance), unless you plan on boring it out, it will never be a 15 horse.

Going from 8 horses to 9.9, an increase of about 25% in horsepower terms, would translate into about 7% more speed at top end (so if you get 15 mph now your efforts would result in almost 1 more mph at wide open throttle - hardly worth the cost of the jet and your time to fiddle with it).
 
hey galamb, thanks for the info. I started reading farther through the specs and started to discover several differences in all kind of areas. Thanks for the info and maybe I'll just bite the bullet and get a larger outboard.
 
That really is the only way if you want better top speed. There just isn't enough that you can do to any given motor to make it perform with a "noticable" improvement.

If your boat is say rated for a 25 horse, get that or you will 1) always wish you had and 2) spend lot's of bucks trying to get whatever you have to perform like a 25 (or whatever).

Most production boats are designed to perform "as designed" with a motor that is at least 80% of their max rated horsepower (so rated for 25 = minimum 20, rated at 90, min 75 (72) etc).

As long as you don't exceed the max horse rating, you will never regret getting the few extra horses - the opposite is never true :)
 
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