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What is needed to change a 99hp to a 15hp

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floydy

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I have a 2005 9.9FMH and I wan

I have a 2005 9.9FMH and I want to upgrade it to a 15hp. I have been told there the very same engine but the 9.9hp has smaller carb jets. Is this true?
 
"I thought about changing my 2

"I thought about changing my 2006 F9.9 to a 15 hp. I asked here. The best answer was that a 50% horsepower increase wasn't really enough. I researched the parts lists at Yamaha's website. There are more differences in the carburetors than just the jets. I thought about trading for a 15 hp 2-cycle. That would give me more power and less weight, but more fuel consumption. Finally I decided to stick with my F9.9 as it is."
 
15hp is max hp for my little b

15hp is max hp for my little boat and the 9.9hp is working too hard on it. i was told that i can change the jets and change the exhaust it would put out 15hp. but i want to check if that's true first
 
I am no expert but I have seen

I am no expert but I have seen this question asked here before as I too have the same Yami outboard. The experts say that a new carb. is required as well as an exhaust part. I think they said $600 in parts without labor. I too may check locally for parts prices. I am looking for a parts engine also.

Drew
 
"You will find by changing the

"You will find by changing the reed box to a 15 hp one you will pick up horse power, I have done this to my own 9.9 and made a big difference.
Hope tis helps"
 
"I thought the F in 9.9 FMH me

"I thought the F in 9.9 FMH meant 4 stroke. My F9.9 is a four stroke. If a 9.9 FMH is a two stroke, please ignore my post above."
 
look at yamahas web site and y

look at yamahas web site and you will see that there is a difference in bore from the 9.9 to 15. 8hp bore is same as 9.9hp so its not possible on the four stroke just the 2 stroke
 
My 2006 F9.9 and the 2006 F15

My 2006 F9.9 and the 2006 F15 are both the same bore and stroke (2.32" x 2.32"). My owners manual is for both motors. Yamaha has changed models since then. So it is possible on a four stroke 2006 F9.9 to convert it to a F15. I decided it wasn't cost effective. This thread started with a 2005 motor. Not the present model listed on Yamaha's website.
 
"Mine is a 9.9 fmh two stroke,

"Mine is a 9.9 fmh two stroke, the ft9.9de is the four stroke. All the spec's are the same for the 9.9hp and the 15hp .(bore size /displacement)etc."
 
"The carbs are the same, chang

"The carbs are the same, change the reed box and reeds. I have done this on the same model. much better"
 
"I have just bought a 2007 9.9

"I have just bought a 2007 9.9 2 stroke and checked out the parts list on the Yamaha site. The only two parts that are different are the reed box and the decals. I checked with our local Yamaha service dept. and was told that they would change the reed box for me but suggested that I wait until the warranty period was up, next June. They freely advised me that the change would give me a 15 hp engine with a 9.9 cowling; a nice feature in horsepower limited waters
"
 
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