9.9 to a 15 hp?

[mkeller]

Somewhere I read that you can turn a 9.9 into a 15 hp motor by changing out the jets in the carb because they are the same just carb is set up different, is this true? If so, does it have to be a certain make, model, or year? Have any of you done this or heard of this?

[KCMO CRAPPIESLAYER]

yes it is true, my dad bought a 9.9 johnson in 87 and had it, what he called boarded out the carb. to a 15 i wish i could tell you more but i don't know much about it just know you can do it. my pop's is up fish'n the big pond in the sky so i can't asked him but we were the fastest 9.9 on the lakes sure someone will have more info, good luck!

[siscoken]

As I recall most 9.9 hps were originally 15 hp engines. The reason that they were detuned to 9.9 was to was to fit into the maximum hp laws that are enforced in many of the parks.
I would say the best bet is to find a scrap yard and change up the carb, intake and possible exhaust. (omc for sure)
Ken

[jh_blount]

The only difference on an OMC 9.9 and a 15 is definitely the carb. Dont really remember on the merc side.

[wefish]

Same on Mercury, a descent mechanic can do it very quick and easy.

[joewildlife]

It ain't always so simple.

read here: http://www.smalloutboards.com/modifications.htm

sometimes it is more than the carb, it can be the intake and exhaust as well. On my Nissan 9.9 buying just a throttle cam was supposed to make it a 15. In fact, the cam on the 9.9 didn't open the throttle all the way. I replaced the cam, then the motor was able to operate wide open. Did it make a difference? Not hardly. Not 50% power increase for sure!

this is what I used for my Nissan. http://www.internetoutboards.com/partdetail.asp?id=505

Also, a late model 9.9 is twice the motor of a 80s model in my experience..

[Bullsprig]

you might be surprised as to the increase. you could be running a good set up for the 9.9 and the extra power will not show all that much change in speed. A friend has a stock 15 merc and his brother has a 9.9. they run side by side for miles.

[Barnacle Bill]

It costs about $800 to change a Johnson 9.9 to a 15. If you put more in (Carbs) you have to be able to get more out. ie reeds, exhaust tuner, etc. The best way to tell is to put a parts list side by side and start comparing. Bullsprig hit the nail on the head. Changing your set up will help more.

[FisherMike]

This being from Service Techs, I have to go with this.

http://www.themarinedoctor.com/cgi-b...num=1176222460

Wheres Papasage when we need him.

[mkeller]

good info. fishermike, thanks