Evinrude 9.9 To 15 Hp Conversion
To reiterate, when doing a conversion from 9.9 to 15 hp, yes you could just change the carburetor, and depending on the year of motor you may have, it may equal what the factory did for that year. We test many 9.9hp and 15 hp outboard motors on our test boat. We do experience some power differences between the two engines but not enough to risk damaging the outboard.
The 9.9 and 15hp motors are exactly the same other than carb venturi. 9.9 is 5000 rpms and 15hp is 6000 rpms. Keep it under 5000 rpms and enjoy your time on the water.
I agree leave it alone and have fun. A decent experiment would be to have both a running 9.9 and a running 15 HP motor, GPS the 9.9, then switch the carbs, then GPS the 9.9 with the 15 HP carb. Then do the same with the 15 HP on the same boat (and same prop).
General info on the conversion of a 9.9 to a 15. Lots of mis-information out there. A 9.9 is a de-tuned 15.
There are NO porting differences. We performed the full conversion to a 15+hp including the carburetor, leaf-valve spacers, and polished 15hp exhaust tube. This engine turned out to make so much power that we had to INCREASE the propeller pitch to the maximum offered 11" (9"x11") to keep it from over-revving.
To turn the 9.9-HP engine into a 15-HP engine may require more than just changing the carburetor. Also, in the carburetor you may only need to change the jets; you may not need an entirely new carburetor. When they went to the actual tuned exhaust, which really helped the mid range, it was not only a carb change but the cylinder head also had less compression than a 15.
I want to upgrade my 9.9 Evinrude to a 15 hp engine. I was planning to shop for a used 15hp. Someone told me I can put a bigger carb into the 9.9 to have it as fast and powerful as a 15hp.
Is that true? Where can I find a carb? Any help is appreciated. Most 9.9's are simply a detuned 15. the real difference is about 500 rpm on the top end.
There is no other difference between the engines, except for some different jets in the carb.
