Johnson 9.9 to 15HP conversion

[JRegier]

Hey everyone, long time no see!
I've finally cycled back into working on outboards and picked up a mostly complete but seized 1983 Johnson 9.9, model J10SELCTC for $40.

I was able to free up the motor and I'm just trying to go over what the motor needs but thought for giggles let's see what happens when I try to start it.

Well, it coughed to life and died almost immediately. I pulled the brand new plugs which were covered in a bit of gunk but no fuel smell on them.
I pulled the carb and to my annoyance it looks like a 15HP carb on it, according to the tag in the picture (link in the bottom). Just wondering what the throat size was supposed to be on a 15 vs 9.9 so I can see if it's the original carb or if someone tried to convert it at one time.
Also, if it does turn out to be a 15HP carb, what should I look for to see if the did a proper conversion or not? I know I've read something about a tuned exhaust system for the 15HP, just wondering what it all looks like.
Thanks in advance.

Pics:
https://m.imgur.com/DfDt8o7,czkqHe6

 

[flyingscott]

Take a pic of the choke side of the throat. If it is a 15 hp carb run it the way it is.There are no tricks to run it they are a direct replacement.

 

[JRegier]

I'm convinced it's a 15HP carb.
My main concerns are poor idle and fouling plugs.

http://m.imgur.com/PnedOM4

 

[flyingscott]

It will be fine.

 

[scout-j-m]

Off the top of my head the only difference aside from carb and the tuned exhaust are reed shims. Checking the exhaust tube would be worthwhile since its probably in your best interest to pull the powerhead anyways and replace the cooling water grommets. But either way it won't hurt to not have the tuned exhaust. I have an 82 model 9.9 and 15 and put the 15hp carb on the 9.9 and it ran fine I just didnt achieve the full rpm increase of a true 15hp.

 

[JRegier]

Thanks for the info, guys