Searching - and Confused 1998 9.9 2-stroke Carb Question

[M.A.CCruiser]

1998 Merc. 9.9 ML 2 Stroke - 0G646082,

I've read through many threads about the 9.9 to 15hp conversion on this site and others. I've seen posts about exhaust tubes and carbs, just carbs, carb and prop (which would seem likely because of extra power). I've seen details on the 4-stroke. But the actual part numbers of it all seems to elude me. Everyone says to check the parts diagrams. But even when i do that, it shows me 3 different carbs! So i am hoping someone can please assist.

I've got this 9.9 pushing a 14'10" fiberglass "skiff" i would call it. And with me (220 lbs) and my daughter sitting in the back, it wont get onto plane. If i stand up and lean forward it'll get on fine, if shes sitting upfront (on the floor, which isn't comfortable of course) it'll plane. I debated weight distribution, but we normally don't go out with more than some waters and 2 fishing poles. so theres not much to distribute. I think a little extra power and MAYBE a 4 blade would get it done. So i ordered the 4-blade, but i'm not confident.

So i would like to start looking into this carb swap for a bit more power as i am confident that a 33% power increase would handle the issue.

Thank you again for your help!

 

[RCO]

A 4 blade prop with the same pitch isn't going to make much if any difference. It may even slow you down a little. The late 2 stroke 9.9 and 15 have different crankshafts, pistons, etc. A simple carb swap isn't going to do it. I would suggest trying a prop with a little bit lower pitch, or bite the bullet and buy a bigger motor.

 

[JerEazy]

Well the 4 blade is 1 pitch lower than the existing 3 blade. Considering that smaller engines react more drastically I figured that should keep my RPMs about the same.

speed isn’t so much the concern. More looking to get out of the hole faster without having to stand up and lean into it.

Also, pretty sure the 98 is the same as the early 90s, at least that’s what the parts sites keep showing.

 

[flyingscott]

Have you done a link and sync? 4 Blade props generally run 2" in pitch less than a 3 blade.

 

[M.A.CCruiser]

no sir - i have not done a link and sync. There's no issues with how it's running if i have my daughter sit up front. But for obvious reasons she doesn't want to sit on the floor, and i don't want her getting up and walking back to me while underway.

i debated the 2 pitch adjustment (it's what i would have/ and have done on my other boats) but what i read says the smaller engines react differently and more drastically to pitch changes than the larger engines. If it doesn't work, then no harm no foul - can keep it as a spare.

I ordered a tiny-tach to keep an eye on things. didn't feel like swapping the one from the golf cart.

checking the parts diagrams again, i think i found the carb. Under the cowl it shows i have the 9.9/15 engine. I read through the mercury service manuals i can find oinline and it shows the same specs on the stroke etc between the 9.9 and 15. So looking at this link

https://www.boats.net/catalog/mercu...hp/0d281000-thru-0g760299-usa-cat-90-81128694

i searched the 9.9/15 as opposed to just the 15 or the 6/8/9.9

and then here https://www.boats.net/catalog/mercu...rb-9-9-15-usa-s-n-0g112450-bel-s-n-9831800-up

i clicked the 15hp carb. Looks like that, then maybe the gasket.

Even says it'll fit the 9.9

https://www.boats.net/product/mercury/9726A5?ref=596269c1d94a2213c7f8fb9edd6ae5bb4fbcba2f

 

[Sea Rider]

Check if current OB matches posted pic, if so. It's a rebadged Tohatsu and the 9.9 to 15 HP conversion is peanuts cost...




Happy Boating

 

[JerEazy]

Negative sir - doesn’t look like that. Sorry for the dark picture.

 

[flyingscott]

You have a Mercury built motor. Around 93/94 the 9.9 started being built on the same block as the 15 hp motor.

 

[JerEazy]

Just realized apparently I have 2 logins here - one my phone uses and the other my desktop. M.A.C. And JerEazy are both me. Sorry for the confusion.

so yes they are the same engine basically. So is my assumption that putting the 15hp carb on (along with a new gasket) is really all that’s necessary to give it that extra umph?

 

[flyingscott]

You will have to compare parts side by.side. It could be just a carb or you may need more.

 

[JerEazy]

Rgr that.

Ill keep eel an eye for parts. Better to buy and rebuild a used than spend $300 on a new on a whim

 

[Sea Rider]

When changing just carb from a detuned engine having same CC powerhead, the higher HP one needs more time advance in order to get the max HP out of them. The tech issue is : more fuel intake needs more time advance to compensate internal combustion. That info is usually posted in the Service Manual unless manufacturer wants to keep it as a Top Secret and avoid boaters upgrading ther engines as there are legal issues involved.

Happy Boating

 

[flyingscott]

When changing just carb from a detuned engine having same CC powerhead, the higher HP one needs more time advance in order to get the max HP out of them. The tech issue is : more fuel intake needs more time advance to compensate internal combustion. That info is usually posted in the Service Manual unless manufacturer wants to keep it as a Top Secret and avoid boaters upgrading ther engines as there are legal issues involved.

Happy Boating

That is not always true at all!

 

[Sea Rider]

That is not always true at all!

Your post doesn't say much, can you deepen the topic for the audience.

I don't like to give I think, assume, word of mouth tech answers. Happen to have several different outboard brands Service Manuals and when swapping carbs states different time advance settings for next HP ranges with same CC powerheads.

Have tested several same CC upgraded HP- OB's with swapped carb, with factory delivered time advance settings and the upgraded HP setting and the agility and faster acceleration achieved was very notorious while the detuned timing gave a very slow acceleration comparing both settings.

Happy Boating

 

[flyingscott]

Mercury 18-20-25 conversion carb and exhaust tuner or some combination of the 2. No timing adjustment.
Omc 9.9-15 hp conversion carb mostly and tuner if you want. Timing is fixed as the timing stop is cast into the block and not adjustable.
Mercury 6-8-9.9 conversion carb and tuner no timing change.
Mercury 9.9-15 hp.conversion carb and tuner no timing change
And depending on which ignition the Ops motor has the timing curve is in the cdi box with no adjustment.

 

[JerEazy]

kind of goes back to my original post - any help with part numbers would be GREATLY appreciated. I can't seem to narrow down which carb is going to do it, and when you say "tuner" i'm assuming something with the exhaust?

My motor is a 1998 2-stroke 9.9ML serial # 0G646082