how do i convert my yamaha 9.9hp to 15hp

[jayhedges]

hi there everyone i have a 2002 model 9.9hp yamaha, i am requiring more power from my motor because i have a heavy tinny and it struggles to plane with two people and minimal gear, have been looking around on other forums and searching the net, i have come to the conclusion that adding another reed valve to the two reed valves already installed, is all that is required to make my 9.9hp a 15hp
hoping anyone with knowledge of this can help me in any way
cheers jay

[almetelo]

Depends....

What is you motor model, code and S/N?

[boscoe99]

Everyone seems to be looking for a silver bullet.

Here is what to do.

Go to http://yamahamc.partsandwarranty.com...TOKEN=49451971 and then on the parts catalog for your 9.9HP two stroke. Then, find the equivalent 15 HP two stroke, and open the parts book for it.

Open each illustration for each of the two motors. Compare the part numbers used on your 9.9 two stroke with the 15 two stroke. Whenever you find a power producing related part, then that part will have to be purchased and installed in your motor.

Just for kicks I compared a 9.9MSHC and a 15MSHC. Surprisingly enough, the only difference I saw is, as you mentioned, the reed valve assembly.

I then looked at the carburetor idle mixture settings for the two models. Surprisingly enough, they are the same.

[jayhedges]

Everyone seems to be looking for a silver bullet.

Here is what to do.

Go to PMPro Consumer and then on the parts catalog for your 9.9HP two stroke. Then, find the equivalent 15 HP two stroke, and open the parts book for it.

Open each illustration for each of the two motors. Compare the part numbers used on your 9.9 two stroke with the 15 two stroke. Whenever you find a power producing related part, then that part will have to be purchased and installed in your motor.

Just for kicks I compared a 9.9MSHC and a 15MSHC. Surprisingly enough, the only difference I saw is, as you mentioned, the reed valve assembly.

I then looked at the carburetor idle mixture settings for the two models. Surprisingly enough, they are the same.

thanks mate, that is a great help to me, i also looked on that site you linked, and it was as you say all identical,besides the reed valves which need to be changed, so i thank you very much mate for your great help, i will be ordering parts later tonight, thanks alot jay

[laflaone]

It is my understanding that you also have to change the jets in the carburetor.

[boscoe99]

It is my understanding that you also have to change the jets in the carburetor.

While this may be true of some models, according to the Yamaha parts catalog the 9.9MSHC and the 15MSHC use the same carburetor and same jets.

You do know that you are responding to a six month old post I presume.

Would be nice if the guy doing the mod to his motor reported back to us the improved performance, if any, that he got from changing the reed valve set.

[ausnoelm]

Also remember that going from 9.9 to 15HP is a 50% increase, do you think reeds alone will give you 50%? even though the parts may look the same (by part number) sometimes, manufacturers only supply the (in this case) 15HP part for certain things, because the 15 will work fine in the 9.9, but the 9.9 part will not work in the 15, well.. not without maybe running lean or something, may not be the case, but it does happen like that.

[arny]

No need for buying new reed valve.Just open the stopper lips for the reed blades to 6mm opening,can be done with a wise grip.Som modells have a trottle limiter on trottle link,can easely be removed.Thats all,no re-jetting etc.

[boscoe99]

Also remember that going from 9.9 to 15HP is a 50% increase, do you think reeds alone will give you 50%? even though the parts may look the same (by part number) sometimes, manufacturers only supply the (in this case) 15HP part for certain things, because the 15 will work fine in the 9.9, but the 9.9 part will not work in the 15, well.. not without maybe running lean or something, may not be the case, but it does happen like that.

According to Yamaha, it will.

Any Yamaha parts that carry the same part number are one and the same part. They are form, fit and function identical. If there are any changes at all then a different part number gets assigned.

[chris1542]

Im in the process of doing the same thing, and I was wondering if I needed the whole reed valve assembly, or just the reeds themselves? Mine is a 1987 9.9SH.
Also is the carb the same other than the jets? I thought I read somewhere that the carb was a few mm bigger for the 15.
Thanks

[rodbolt17]

typically the 9.9 has 2 reeds on the reed block and the 15 had 3.
they did it that way for some years here in the states.
with the correct test prop you can actually see the 200 RPM difference on the tach.

[chris1542]

typically the 9.9 has 2 reeds on the reed block and the 15 had 3.
they did it that way for some years here in the states.
with the correct test prop you can actually see the 200 RPM difference on the tach.

Is the block the same? Can I just buy the reed set and use the existing reed block?

[rodbolt17]

the engine block carries the same part #.
on the reeds.
only if you can figure out how to mount 3 reeds on a 2 reed block.

[chris1542]

the engine block carries the same part #.
on the reeds.
only if you can figure out how to mount 3 reeds on a 2 reed block.

So I need the new reed block, how about the carb? Do I need the whole carb or can I just change the jets?
Thanks

[boscoe99]

So I need the new reed block, how about the carb? Do I need the whole carb or can I just change the jets?
Thanks

What does the Yamaha parts catalog tell you that is needed?