Hot Rodding a 9.9 to 15 HP

[Chris in Indiana]

I've got a Mercury 9.9, Ser 0B398065 which was built in 1989. First year for the 9.9's I beleive. Has anyone out there ever hot-rodded one of these? I have read posts on Craigslist where people claim to have installed a carb from a 15hp merc outboard but I'm wondering how intricate such an operation is. I have an inflatable boat that's somewhat sensitive to weight so I would love to boost the power without going to a significantly heavier motor.

 

[rg2]

Re: Hot Rodding a 9.9 to 15 HP

I've heard/read the same things Chris. The common answer by the experts, or at least those I consider experts, is LEAVE IT ALONE. Apparently there is more to the conversion than just simply swapping carbs. Exhaust ports are a issue as well and if everyhting is not addressed then you may do more harm than good to your motor. When I was younger, about 30+ years ago I had an evinrude, brand new from a dealer, that had the carb swapped. It hard to make a true comparison after all these years but I'm not so sure that motor was any more powerful than the true 9.9 Mercury I have now.

Good Luck.

 

[Bartine]

Re: Hot Rodding a 9.9 to 15 HP

You'll have a hard time getting an answer on this around here. No here will give up their secrets. My suggestion to you is to look at the parts diagram for the two motors and see what is different. I upgraded my 75hp four stroke to a 90hp by simply swapping carbs. EVERY part was the same except the carbruators (bigger throats and different jets inside). I know it made a difference because I had to get a higher pitch prop afterwards.

 

[ONERCBOATER]

Re: Hot Rodding a 9.9 to 15 HP

specific things to look at would be carb, pistons, reeds, reed stops (and if there are spacers) pipe..... my guess is that should about cover it...provided of course that they are the same CC displacement.
Sean

 

[Chris in Indiana]

Re: Hot Rodding a 9.9 to 15 HP

Thanks for the suggestions folks, very much appreciated. I don't want to spend a ton of time on the conversion, or smoke the motor, but if it's just a carb swap I'll try it. It sounds like the best thing to do is look up part numbers online and see what's different between my 9.9 and a 15 from the same year.