1999 Mercury 9.9 to 15?

[Anthony1323]

(I was mistaken when I wrote this it’s actually a 2000 sorry for the inconvenience) Hey I was looking into this a few months back but never could really get anywhere so I thought I’d ask for help from someone else. I was wonder if I could turn my 2000 Mercury 9.9hp 2 stroke into a 15hp, like what would it take? Any information will be very appreciated thank you.

Serial Number: 0T079978

[GordMay]

Greetings and welcome aboard the CF, Anthony.

[Dymaxion]

An older 9.9 Evinrude I worked on could be upgraded to 15 by switching to a 15 carb. Around here motors larger than 9.9 require the boat to be registered, hence the detuning.

[svHyLyte]

We have a 15hp Merc 2-stroke purchased in early 2002 that is likely the same as your engine. As described by the dealer, the only difference between our engine and the 9.9 hp version, at the time, was the carburetor, in the fashion commented on by Dymaxion, above.

FWIW...

[CarinaPDX]

The 6, 8, 9.9, and 15 were essentially the same engine, weighing between 73# and 75#. However, the differences are more than just the carburetors. The ports in the cylinders are different sizes, and IIRC the 15hp has a tube that runs the exhaust down inside the lower unit while the smaller engines just dump the exhaust in at the top of the lower unit. There may be other differences. You should get a copy of the parts manual and look for the differences there. I really doubt it is worth the effort this late in the game.


Greg

[LeaseOnLife]

Originally Posted by CarinaPDX

The 6, 8, 9.9, and 15 were essentially the same engine, weighing between 73# and 75#. However, the differences are more than just the carburetors. The ports in the cylinders are different sizes, and IIRC the 15hp has a tube that runs the exhaust down inside the lower unit while the smaller engines just dump the exhaust in at the top of the lower unit. There may be other differences. You should get a copy of the parts manual and look for the differences there. I really doubt it is worth the effort this late in the game.


Greg

I don't think this is all correct. IIRC, the 6, 8, 9.8 2-stroke Tohatsu/Nissan/Mercury are based on the same engine, top end as well as lower end.


The 9.9 and 15HP were bigger and heavier. I can't speak for the 9.9 and 15HP, but I was able to convert a 8 to a 9.8 with just changing jets. I had access to a parts manual and compared the three columns for 6, 8, and 9.8 HP, ordered the 3 jets. Plus the prop has a different pitch, but I opted to keep less pitch for getting up to plane quicker.



Similar, if someone has access to a 9.9-15HP parts manual from back then, it should be possible to find the differences. It might be more than jets...

[CarinaPDX]

I didn't remember the breaks in sizes, but overall my comments were correct for the range of power.

Up to S/N#G112449 the 8 and 9 shared the same block (port size) and the 6 and 15 were each unique; from S/N#G112450 the 9.9 shared the same block as the 15 - which covers the 1999 model. So no worries there.

The carburetors were also different until the same S/N break, after which the 9.9 and 15 used the same carburetor design with differing throttle valves and shafts. There is a Restrictor Kit P/N 12750A1 (old) mentioned but without any description or call-out on the parts explosion, so do some research there.

Finally, the exhaust system is different as I described earlier. The 6 and 8 just dumped the exhaust into the lower unit. The original design of the exhaust for the 9.9 had a 1" diameter exhaust tube and the 15 had a 1-1/8" diameter tube. Later (Design II) apparently uses the same tube for both the 9.9 and 15. I have no indication as to when this change occurred.

Greg

[Karltheboy]

If yours has the round choke knob tgen its just the carb that is different