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9.9hp upgrade?

Discussion in 'Boats and Motors' started by elkhtr, Aug 10, 2007.

  1. anyone upgrade their 9.9 to 15hp by buying a new carb? I have read about it, but have a few questions.

    Is it worthwhile? Is there a substantial increase in power?

    Would the motor still be as reliable?

    Any recommendations would be appreciated.

    I presently have a 1999 Johnson 9.9. My 16' smokercraft goes 15mph when i am by myself. Wondering what I could expect if I upgraded.


    I have a 1976 johnson 9.9 that has a 15 hp carb on it and when i rebuilt the motor almost 2 yrs ago i also added boysen power reeds to the motor.the 15 hp carb was on it already when i bought the motor.

  3. BigDaddy300

    BigDaddy300 multi species angler

    I was told that it was not a significant difference. My 9.9 had the 15 carb when I bought it so I have nothing to compare it to. There was a site that talked about the switch. If I can find it I will post it.
  4. alan farver

    alan farver purple raiders softball

    i had it done to my 9.9 mariner.not much difference accept it uses more gas.i also changed the prop that helped more then the carb and was not near as expensive
  5. ezbite

    ezbite the Susan Lucci of OGF

    no i have not done a carb switch. the prop switch makes sense to me.
  6. I did the 9.9/15 change on my 2000 9.9 Johnson and feel it was a very worthwhile modification.
  7. thanks for the replies everyone.
  8. any recommendations on what props to look at that would increase performance significantly?
  9. alan farver

    alan farver purple raiders softball

    i went from a nine pitch to a seven pitch.that is what was suggested to me
  10. GPtimes2

    GPtimes2 Oh Deer

    I would find out what RPM your running at full speed with a normal load (what you mostly have in the boat) before changing anything. I would get or borrow a tach first. Once you know your RPM, it will be your guide as to changing the prop and/or carb. You may be able to do both.:)
  11. I have alot of experience with this. I have done upgrades to many 9.9 Johnsons and many others. The carb change is a must. Just look at the carb throat and you can see the difference. I open the motor up and port and polish the intake and exhaust. When these motors are made. The casting leaves an edge of metal that impedes the air flow. Use a dremmel tool and take the edge out. If you are a nut like me, have the head milled 30 thousands. This will add compression. Now you have to match the HP with boat weight and come up with a prop that will allow you the max of 7000 RPM's.Your boat now is limited to 5500 rpm's. My motor has ran for years this way. I troll for eyes and fish bass tourniments. I was told by a very good source that these motors can run this hard but not to let it go over 8000 rpm's. They will come apart. Anything that you do will help. Just the carb and the prop. will help. Remember rpm's equals speed. You have to get a prop that gets you out of the hole and them reaches top speed. This all comes for someone that races 9.9's on small boats.
  12. thanks for the info. I have some work and learning to do before I undertake this.