converting 95 Johnson 9.9hp to 15hp

[Gustofson]

I have this motor and I need more speed for trolling Muskies. I have heard that the only difference is the carburator. Is this true? Any reason I should not do it?

 

[kbait]

Re: converting 95 Johnson 9.9hp to 15hp

Not sure on the carb swap, but you are apparently using this motor for a kicker? And a very heavy boat? Consider a lower pitched prop, especially if it seems like the motor is lugging along at full "muskie" speed. Standard prop is about 9x10".. a 9x8 or even 9x7 will get you up in rpm's to a much better hp range..
Check out what prop you have, and check at the top of this page under parts, then props. Really nice prices on this site!

 

[tashasdaddy]

Re: converting 95 Johnson 9.9hp to 15hp

there is not an dyno proof in that statement. there is a big thread on this, please use the search function.

 

[mikesea]

Re: converting 95 Johnson 9.9hp to 15hp

i believe the earlier engines had a simple carb change,but,the later engines had a different exhust configuration,it makes me wonder if the earlier engines actually had 15 hp,if the only differance was the wider throat carb

 

[14ftgrumman]

Re: converting 95 Johnson 9.9hp to 15hp

Very easy and worry free..


Sell the 9.9 and buy a 15.

Also most times the path of least resistance.

That being said, I'd try re-propping the motor, as above. Good tune up, rebuild carb, and a de-carb with SeaFoam.

 

[kbait]

Re: converting 95 Johnson 9.9hp to 15hp

no proof, t's daddy.. but it makes sense to use a short prop if it's a kicker on barge-like fishing boat anyway, just for performance. But I cannot say for certain that it would be any faster. I can assume..

 

[bktheking]

Re: converting 95 Johnson 9.9hp to 15hp

i believe the earlier engines had a simple carb change,but,the later engines had a different exhust configuration,it makes me wonder if the earlier engines actually had 15 hp,if the only differance was the wider throat carb

The 15 revved higher which leads me to believe they had different power packs, they also had a shim in the reeds to allow for more fuel delivery. Plain answer is, buy a 15 if you want 15.

 

[jay_merrill]

Re: converting 95 Johnson 9.9hp to 15hp

As TD said, there was a rather lengthy thread on this topic, but I couldn't find it. You may want to use the search function, to see if you have any luck.

More often than not, however, its not as simple as a different carb or high speed jet.



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