Re: Yamaha 9.9 to 15 hp
To anyone considering the conversion from 9.9 to 15, I can confirm that the difference is the carburetor and the reed valve assembly. A side by side comparison of the parts in my hands confirms the following:
The 9.9 reed valve assembly has a total of 4 reeds and a blank space where the other 2 reeds would be. The 15 HP reed valve assembly has 6 reeds and uses all of the "available space".
As previously stated, the throat of the carburetor is noticeably larger for the 15 HP.
Of course, all of the above allows more air and fuel into the engine, thus creating more power.
Don't forget that producing more power won't do much good unless you also change the prop to take advantage of it.
I bought a solas 11pitch prop and that should do the trick.
I have completed the conversion on my 1987 9.9 but I have not had the chance to try it out yet. I can't wait.