Nissan 4 stroke NSF9.9B2 to 15 or 18hp conversion

mhenry27

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Hi

Thanks to all of the previous posters and especially the responders for the knowledge i have gained from this forum on this matter and many others

Have a chance to get a 2002 4 stroke NSF9.9B2 and looking at upgrade options. After perusing the forum it seems

I can upgrade to to a 15 with a simple carb change.

I can upgrade to an 18 with carb change, air intake and ? additional parts(where can i get that info)

Should it be automatic or an option(if I am not happy with improvement) to check WOT RPM with a tach and make adjustments or is this only for the cam change/arm adjustment for the 2 stroke?

Then if i am still not happy possible prop change?

Thanks for any help and guidance

mike
 

Sea Rider

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Welcome,

Do you already own an OB or plan buying those mentioned ?

Those are obsolete OB's. MFS 9.9B2 carb is different than the MFS15B2 model, but 15B2 is same style as MFS 18B. Most parts being obsolete are NLA. Better invest wise and go for a newer 2 or 4 strokes models.

Happy Boating
 

mhenry27

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Thanks for the reply
.
I am supposed to pick up the motor in a few days. A very good buy either way but i wanted more out of it of course.

Is it because of the year of my motor(2002) ? I ask because i have seen comments on other posts relating to 2003 and 2004 nsf9.9b2 model upgrades suggesting only a carb change to the 15(new carb part #3R3035002M still available). I was not so sure about the upgrade to the 18 but thought that was possible as well just not sure of all the parts.
 

pvanv

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Year is irrelevant. Model/serial is everything. When the 9.8 4-stroke made the heavier 9.9B2 obsolete, it was eventually dropped from the lineup, and the newer, larger 15/20 replaced the 9.9/15/18. Depending on serial, the inlet manifold (NLA new) is identical, so the carb (and silencer) is the hp limiting factor.
 

mhenry27

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It is model NSF9.9B2 3v5-1
serial # 12249

Ideally i wanted to convert it to an 18 but 15 is okay as well.

Thanks for your time and guidance
 

Sea Rider

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Probably will need besides a carb change a timimg adjustment as higher HP needs more time advance, check specs for both OB's.

Happy Boating
 

pvanv

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Probably will need besides a carb change a timimg adjustment as higher HP needs more time advance, check specs for both OB's.

Happy Boating

No. Timing is electronically-adjusted on these. The CD has the advance curve integrated into the circuitry. The same CD fits the 9.9, 15, and 18; no change required.

Just swap carb and silencer. The inlet manifold is identical. BTW, the carb will cost more than $200.
 

mhenry27

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Of course would have preferred the relatively cheap cam upgrade of the two stroke but already had an idea of the cost for the carb and more than content to pay if i get a decent return on performance,

Especially excited to have the option for the conversion to the 18.

Thanks again for the help
 

Sea Rider

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Especially excited to have the option for the conversion to the 18.

Thanks again for the help

Check if 15 HP carb is same for the 18 and if both modles shares same CC powerhead ? If not, convert to 15 HP. There should be an oustanding performance difference, you can always maximize a prop to run top installing an induction tach.

Happy Boating
 

mhenry27

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One final thing i wanted to be clear on after reviewing the posts here(some responses to other threads by pvanv) and the parts list.

Does a conversion to the 18 need a new camshaft specific to the 18?

It is a different model number on the parts list(3v9070100M vs 3R3070100M)and i believe i saw one reply on a different thread but that may have been specific to a problem with the camshaft on the 18.
 

pvanv

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The
3V9070100MCAMSHAFT ASSY, MFS18B-NLA

Is no longer available, so it's a moot point. Is there a slight profile difference? Maybe. The swap up from 15 to 18 is a 20% power increase, but the conversion from 9.9 to 15 is the big gain, (almost 52%). If you want to use the 18 carb, it will work... you just may not develop that last hp. If you want to be ultra-safe, use the 15 hp carb. Then you can continue using your present silencer as well.
 

pvanv

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Check if 15 HP carb is same for the 18 and if both modles shares same CC powerhead ? If not, convert to 15 HP. There should be an oustanding performance difference, you can always maximize a prop to run top installing an induction tach.

Happy Boating
The blocks are identical. All 3 carbs are unique.
 
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