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9.9 to 15

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zackie77

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I have a 1976 evenrude 9.9, is it possible to make it into a 15hp. I believe it"s the same power head. also if I changed props would I get more speed out out of the 9.9. itS on an old sea king 13.5 footer and it will plane only if I put 100 pounds in the front, would a different prop help?
 
On that model, you can increase the hp to 15hp simply by changing the carburetor to the 15hp type.

Changing the prop? You would need a tachometer to see what the top rpms (full throttle) are. For example, if the manual states that full throttle rpms are say (for example) 5000 rpm, and your engine is only obtaining 4000 rpm at full throttle, then yes, changing the propeller would help, BUT if your rpms at full throttle are say 4800 rpm, that's pretty close, about as good as you're going to get.
 
kimcrwbr1 said:
You have tried tilting the motor different right. Bringing the bottom of the motor forward will push the bow down and moving it back will lift the bow up but with a 13.5 foot boat the 9.9 aint gonna go real fast.
Click to expand...

I agree. I have the same motor and I find if I adjust the tilt differently depending on whether I am alone or someone who has ate too many twinkies is sitting up front, it makes a big difference to the plane and top speed. You should play with it and see the difference.
 
If that engine is not running at 6000 RPM it is not a 15 HP.----------It is rated to be 15 HP at full throttle at 6000 RPM.---------Not sure where the " back pressure and slime idea " comes from when talking about the converging ring on the prop
 
I think I"ll leave it alone,maybe I"ll put a doel fin on it and move some of the weight up front. it runs to good to mess with, but thanks for the info, very good stuff.
 
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