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What part makes a Johnson 9.9 to a 15

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Brian4591

Contributing Member
I have a Johnson that I got from a guy it runs but he told me he thinks it's a 15hp even though the cover says it is a 9.9. There is no ID numbers or tag on the motor. I believe it is around a 1984. I looked for parts for both 9.9 and 15 and can not figure out the difference between them. I Have not found any part to be different. Pistons, Carb, Head,Jets,Intake manifold are all the same parts for both. SO WHAT MAKES A 9.9 DIFRENT FROM A 15HP. Trying to determine what hp I have.
 
Well, the differences in the carb throat is the easiest way to tell. The one on the left is 9.9, right is 15. Keep the choke open and take the baffle off and have a look.
9.9_15_carbs_front.jpg
 
Look on the silver disc on the head for the model#. In 1984 I believe the 15 used a different exhaust tuner and reed spacers and they always used a different carb.
 
Venturi and nozzle, high speed jet, intermediate jet (air) inner exhaust tube (tuner), leaf stop spacer? Depending on the model number of the motor there were suttle changes if the displacement is the same then the 9.9 is just a detuned 15hp normally the 9.9 has 500rpm less wot rpm difference also.
 
No need to pull the jet. Just look down the throat of the carb if it has a brass tube running up through it will be a 9.9 carb. The 15 hp carb will not have the tube running through the throat of the carb. Look in post #3 for the pics.
 
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