Converting 1986 Merc 9.9 2-stroke to 15HP?

[zuren]

Has anyone converted a late 1980s 9.9 Merc 2-stroke to 15HP? I've read of guys doing this and from what I understand is that the 9.9 and 15HP engine are the same with the exception of a different carb, or different carb AND exhaust tube (still trying to clarify what I need). I would not mind some extra horsepower. The lakes around me are either no restrictions, or electric only, so a 9.9 motor really is not benefiting me. The boat is rated for 25HP.

I'm weighing the cost and complexity of converting what I already own, VS. finding a 15HP 2-stroke, VS. one of the lightweight 4-strokes (Tohatsu - 94 lbs, Mercury - 99 lbs.). My 9.9 is 70 lbs., so even a 94 lb. Tohatsu may be too much.

So I'm just wondering if anyone has done it? Was it worth it? Would you do it again?

Thanks!

 

[GYPSY400]

Go to marine engine dot com and compare parts between a 9.9 and 15.. if the block and pistons are the same you'll be in luck .
Most likely its the carb and prop, with the possibility of the exhaust pipe needing to be changed.

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[ktoelke54]

Tohatsu/Merc 20hp 4stroke weighs the same as the 15hp. This would be my choice in a new or newer motor, if weight is your primary concern but you want more power. Converting your 9.9 to 15 is relatively simple with lots of info and parts readily available online if you poke around.


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[zuren]

I followed Gypsy's advise and spent time at MarineEngine.com. From what I could see, the block and pistons between a 1986 9.9 and 15 hp are not the same, leading me to believe that a conversion is not feasible, or at least not as simple as I would hope. Then I found a comment in a forum somewhere that it is only the mid-1990s and later Merc 9.9s that can be converted. So based on what I'm finding, I'm not convinced mine can be "easily" converted.

I'm considering saving my pennies and looking into a Tohatsu 15-20HP. At 94 lbs., it is heavier than my 70 lb. 2 stroke, but I'm looking to get my battery and trolling motor up toward the bow. That may be enough for the extra 24 lbs. to work.