1999 yamaha 2 stroke 9.9 to 15hp conversion

[merc16]

Hey guys, i understand the only difference is the reed valve assembly has taller reed stops im just looking everywhere for that part number and cant find a proper answer, on the website theres 2 reed assembly part numbers (63V and 63W) but i dont know which one is for the 9.9 and which one for the 15

 

[Sea Rider]

What's the current 2 stroke model, 9.9 what ?

Happy Boating​

 

[merc16]

What's the current 2 stroke model, 9.9 what ?

Happy Boating​

Thanks for the reply! Its a 1999 9.9MSHX model (2 stroke obviously) lol

 

[boscoe99]

It is all within the Yamaha USA parts catalog. Can be seen at www.yamahaoutboards.com

 

[99yam40]

just as I thought the 15hp reed cost a little bit more that the 9.9

 

[merc16]

It is all within the Yamaha USA parts catalog. Can be seen at www.yamahaoutboards.com

Thank you sir it was specified as to the 63W was for the 15 i cant find any other differences, timing, fuel ie.

 

[Sea Rider]

A 2 stroke 9.9 HP motor when upgraded to a 15 HP one usually needs more time advance as will work with more fuel intake, check with the Yams's Service Manual if need to perform a new carb/time advance synch or not ?

Happy Boating​

 

[boscoe99]

Thank you sir it was specified as to the 63W was for the 15 i cant find any other differences, timing, fuel ie.

Neither could I. I looked at every line item of every page in the two parts manuals. Only difference I saw is the reed valve assembly.

Surprised me actually. I was expecting the CDI assembly to be different.

 

[boscoe99]

just as I thought the 15hp reed cost a little bit more that the 9.9

That is interesting. Both have the same MSRP but different boats.net prices.

Both of them still being available surprised me also.

For 50% power increase and the cost being what it is I would give it a try.

 

[Sea Rider]

That is interesting. Both have the same MSRP but different boats.net prices.

If you check both parts there, clik on each 9.9 and 15 HP parts and will open a posted pic which are identical. Probabbly the reeds on the 15 are bit hardened, thicker, the ports and reeds are bit wider whatever ?

To check the power increase will need to tach and GPS the standard 9.9 and upgraded 15 on a wot run on flat calm water cond and check if there's a real rpm/speed difference while all other parts remains same for both and only have swapped a 15 reed valve into a 9.9...

Happy Boating​

 

[99yam40]

If you check both parts there, clik on each 9.9 and 15 HP parts and will open a posted pic which are identical. Probabbly the reeds on the 15 are bit hardened, thicker, the ports and reeds are bit wider whatever ?

To check the power increase will need to tach and GPS the standard 9.9 and upgraded 15 on a wot run on flat calm water cond and check if there's a real rpm/speed difference while all other parts remains same for both and only have swapped a 15 reed valve into a 9.9...

Happy Boating​

only true way to find out would be to dyno the motor before and after the modification.
with a 50% increase in HP would a different prop be needed also

also it was mentioned the reed stops were different allowing the reeds to open more

 

[boscoe99]

If you check both parts there, clik on each 9.9 and 15 HP parts and will open a posted pic which are identical. Probabbly the reeds on the 15 are bit hardened, thicker, the ports and reeds are bit wider whatever ?

To check the power increase will need to tach and GPS the standard 9.9 and upgraded 15 on a wot run on flat calm water cond and check if there's a real rpm/speed difference while all other parts remains same for both and only have swapped a 15 reed valve into a 9.9...

Happy Boating​

Not following you on the parts being identical. Different part numbers. Must be some physical differences.

 

[Faztbullet]

The reeds are less restrictive due to stops and larger intake area...

 

[Sea Rider]

Only true way to find out would be to dyno the motor before and after the modification, with a 50% increase in HP would a different prop be needed also,also it was mentioned the reed stops were different allowing the reeds to open more...​

How would you dyno the motor ? To validate that simple and cheap conversion will need someone to chime in and post pics/measurements of both 9.9 and 15 HP reed valve assys and check their physical differences, one who have actually done the conversion including both motors water wot tests rpm and gps achieved parameters with same boat, same load and current prop. Both 9.9 & 15 HP reed valve leafs are the same code, so the 15 HP holes/ports could be different including the reed stops to allow more air/fuel intake.

There should be a $ 350-500 price difference between a MSHX 9.9 and MSHX 15 HP motors, do you think that by a simple $ 73 reed swap can fully convert a 9.9 to a 15 HP motor, there must be something else hidden there, Yam and many other motor fabricators doesn't want boaters to upgrde their next HP motors for peanuts cost as there's a price difference to pay. Busines are Business....

Happy Boating

​

 

[99yam40]

How would you dyno the motor ? To validate that simple and cheap conversion will need someone to chime in and post pics/measurements of both 9.9 and 15 HP reed valve assys and check their physical differences, one who have actually done the conversion including both motors water wot tests rpm and gps achieved parameters with same boat, same load and current prop. Both 9.9 & 15 HP reed valve leafs are the same code, so the 15 HP holes/ports could be different including the reed stops to allow more air/fuel intake.

There should be a $ 350-500 price difference between a MSHX 9.9 and MSHX 15 HP motors, do you think that by a simple $ 73 reed swap can fully convert a 9.9 to a 15 HP motor, there must be something else hidden there, Yam and many other motor fabricators doesn't want boaters to upgrde their next HP motors for peanuts cost as there's a price difference to pay. Busines are Business....

Happy Boating

​

the 9.9 is just a 15 that was modified at the factory to meet requirements on HP restricted lakes/ponds.

dynoing a motor is the same for any type of motor.
not many have the equipment to do it, but it shows HP and torque output curves

most people swear how they modified motors and increased their output without any proof it did anything

 

[Sea Rider]

Yep, about being a 9.9 which in reality it's a 10 HP motor, just playing with the numbers to meet lake restrictions. Anyway a perfectly modified 15 HP should achieve more revs and slight more top end speed than a 9.9 while carrying more load, if propped towards its max wot rpm the better.

Correct, most people swear how they modified motors and increased their output without any proof it did anything. A wot test before and after mod will tell if any difference...

Bottomline if someone has the Yam's MSHX 9.9 and 15 HP Service Manual, check if the time advanceº for each HP it's mentioned and adjust accordingly along the reed assy swap. But if Yam doesn't want boaters to upgrade their next HP motors as in this case will simply skip that vital information...

Happy Boating​

 

[boscoe99]

I have compared the 9.9 and the 15 parts catalogs. Only difference that I can see in the reed valve assembly.

I have compared the 9.9 and the 15 service manual. Only difference that I can see is the reed valve assembly.

Would not have believed it had I not seen it.

 

[99yam40]

Yep, about being a 9.9 which in reality it's a 10 HP motor, just playing with the numbers to meet lake restrictions. Anyway a perfectly modified 15 HP should achieve more revs and slight more top end speed than a 9.9 while carrying more load, if propped towards its max wot rpm the better.

Correct, most people swear how they modified motors and increased their output without any proof it did anything. A wot test before and after mod will tell if any difference...

Bottomline if someone has the Yam's MSHX 9.9 and 15 HP Service Manual, check if the time advanceº for each HP it's mentioned and adjust accordingly along the reed assy swap. But if Yam doesn't want boaters to upgrade their next HP motors as in this case will simply skip that vital information...

Happy Boating​

so does the service manual for a 15 have spec that it should run at higher RPMs than a 9.9?
what about a 25 or 30 HP motor?

maybe Boscoe can tell us on the 15 specs

 

[boscoe99]

so does the service manual for a 15 have spec that it should run at higher RPMs than a 9.9?
what about a 25 or 30 HP motor?

maybe Boscoe can tell us on the 15 specs

See the data posted above your message. No change in RPM between the two models. 9.9 and the 15.

Simply seems to be letting more air through the carburetor. Carburetor adds more fuel of course. More air, more fuel, more power.

 

[99yam40]

so if the 9.9 was propped correctly to hit the maximum WOT RPM,
then turning it into a 15 would mean a different prop was needed to Keep the RPMs from over revving that same WOT RPM spec