Johnson/Evinrude 15hp history question...

dfrants

Petty Officer 1st Class
Joined
Jul 26, 2008
Messages
368
I purchased a 1977 Johnson 9.9hp, a buddy said if you change out the carb you can turn it into a 15hp. Which I did. Talking to one of the old service guys at the local shop told me that it really isn't a 15hp. That those older ones only produced 12hp. That I need to find a 1984 or newer one that is really a 15hp. That they opened the exhaust porting to produce the extra ponies to get 15hp...is this fact or fiction?
 

flyingscott

Fleet Admiral
Joined
Apr 8, 2014
Messages
7,985
Those motors are a little lower than the newer ones but Exhaust porting was the same all the way through. The difference is the exhaust tuner and reed spacers. You can add those to yours.
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
If both 9.9 & 15 are 250 CC should be same powerhead. Converted a 96- 9.9 HP to a 15 HP, for that needed to swap 15 HP carb , reed valve plate aasy and gaskets to work as a 15 HP. Great difference.

Happy Boating
 
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