Re: Convert 9.9HP to 15HP?
You'd have to get the right parts.
Part of the conversion on Evinrude/Johnsons was the carb - which plenty of places used to offer to upgrade for a fee (and sometimes charge you, but not upgrade), but what they all used to leave out of the equation was that to get 15 hp like the manufacturer did out of them, you had to also find and install the correct exhaust manifold... which no-one ever seemed to do when they sold people on upgrading their 9.9HP.
I'm not sure about mercs, but you've got to do your own research into part numbers for identical year, or series, motors, then inspect what changed from the 9.9 to the 15's if the pistons and powerhead were the same. On motors other than the 'rude/Johnsons it could be an ignition thing as well.
