86 Johnson 9.9 to 15 mod - exhaust tube question

Joined
Apr 19, 2009
Messages
19
Hi all,

I've done a LOT of research on converting a 1986 Johnson 9.9 to a 15 and have in my posession the proper carb, the reed shims and even the exhaust tube. Found them quite cheap, so I'm looking forward to making this conversion soon. I'll be doing my own work and want to make sure I have all the parts I need before starting, which brings me to my question:

Looking at a picture of the 9.9 and 15 exhaust tubes, it appears as though the 15 is shorter, and simply rounded into a tube at the bottom. The 9.9 is moulded square at the bottom and is longer, and it appears as though it either bolts or fits nicely onto something. Is this the case or does it not matter at all?

Lastly, looking at the top view, what's the extra tube at the top left up there for? I'm concerned as it's not on the 9.9..

Best,
Mark
 

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quackaddict1

Petty Officer 2nd Class
Joined
May 30, 2008
Messages
138
Re: 86 Johnson 9.9 to 15 mod - exhaust tube question

That tube looks like a water pickup line, but im not 100% sure.
 

TLL

Petty Officer 3rd Class
Joined
Mar 4, 2004
Messages
92
Re: 86 Johnson 9.9 to 15 mod - exhaust tube question

The exhaust tube of the 9.9 fits tightly onto the bottom of the midsection with a rubber grommet. The 15 round tube simply hangs from the bottom of the powerhead and directs the exhaust thought the midsection. I would think the midsections are the same, but I really haven't compared the two.

The copper tube I believe to be an water outlet for the block. It just hangs from the exhaust tube and allows cooling water to mix witht the exhaust.
 
Joined
Apr 19, 2009
Messages
19
Re: 86 Johnson 9.9 to 15 mod - exhaust tube question

Thanks for the information. So do you think it will just bolt right up and work? Anyone else?

My only concerns at this point are that the 15's rounded and shorter tube won't seal up at the bottom with this grommet, and that the 9.9 doesn't have this water exit tube, so where is my cooling water exiting now, and will it affect anything by me bolting up this new tube?
 

TLL

Petty Officer 3rd Class
Joined
Mar 4, 2004
Messages
92
Re: 86 Johnson 9.9 to 15 mod - exhaust tube question

The 9.9 still spills out water around the exhaust tube, but since the tube is sealed at the bottom the whole midsection fills up with water after the motor is running. This quiets the motor and helps cool the exhaust. There is also water that mixes with the exhaust. On the 15, the water and exhaust is all dumped out togeter and mixes as it leaves the midsection. There is no "wall of water" surrounding the exhaust tube. I think that just changing the exhaust tube would work fine. Since you are increasing the fuel flow into the engine, it makes sense to increase the ability to exhaust too.
 
Joined
Apr 19, 2009
Messages
19
Re: 86 Johnson 9.9 to 15 mod - exhaust tube question

Thanks, TLL. This is the reassuring information I was hoping to see. Cheers!
 
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