Johnson TD 20

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warpedrotor

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Joined
May 13, 2007
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16
Just acquired a Johnson TD 20. Has compression and good spark, I took the carb apart and it's a mess. I have a spare 9.9 carb that has about the same bore. I can build some flanges to adapt it to the intake, but I am wondering about these small lines that run from the carb to a Y shaped connector on the front of the crankcase, one line goes up under the flywheel, another seems to have nothing connected to it, either it had some type of valve or tube connected to it. The middle of the Y shaped connector part has a hole in it with a rotating part visible. What is the purpose of these tubes?
 
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racerone

Supreme Mariner
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Dec 28, 2013
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38,579
That hole is the low speed air fuel intake through a rotary valve ( hole in the crankshaft).-----It should not be hard to find the correct carburetor for that motor.
 
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warpedrotor

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May 13, 2007
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So it looks like I'm missing the valve stem that would come out on the lower right of this Y assembly. Still wondering what the line is that runs up under the flywheel? There are no new parts available for this carb, no used carbs sold as ready to use anywhere. There's great info on how to make your own floats and seals for the primer plunger. I would like to try the 9.9 carb as an experiment, I'm just worried that the line going up under the flywheel has something to do with lubrication?
 
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racerone

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Dec 28, 2013
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Perhaps looking in the wrong places.-----Post an ad on ----aomci-----website.-----Cost you no coins to post a wanted ad there.
 
F

F_R

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Jul 7, 2006
Messages
28,226
Yes it is a lubrication line (sort of). Sorry, but that 9.9 carb simply is not going to work. That motor has two separate and distinctly different induction systems, one for high speed operation and one for slow speed operation. In effect, dual carburetors. The Y part is a very simple and crude "carburetor". It feeds into a rotary valve. So simple and crude that it blows the modern-thinking mind. But they work well.
 
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warpedrotor

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May 13, 2007
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Thanks guys, well I'm missing the low speed adjustment needle too.. there's an excellent video on You Tube explaining DIY carb parts and mods, he had also posted a link to manuals and schematics of the motor explaining that the upper tube is an oil return line from the upper bearing/seal. The rest of the motor is in great shape so it's a keeper, I'll keep it as a winter project.
 
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warpedrotor

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May 13, 2007
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16
Finally back to this, found some parts, ideas for a plastic float and a guy that makes the leather primer seals on line. I was still wondering about the line from the carb to the low speed air inlet or Y connector, am I right that fuel continues to flow through this line after priming (engine running) and is mixed with air at the Y connector?
 
F

F_R

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Yes, in addition to the high speed fuel going from the main carb to the third port system.
 
TN-25

TN-25

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May 27, 2008
Messages
620
The carb comes into operation at lower mid-throttle through to full throttle but doesn't operate at idle or trolling speeds. At idle it operates on that crude Y-block fuel line (controlled by the little L lever) that runs into the crankcase to be pressurized and sent out the port when the time comes. Technically you could run only on the low-speed "jet" or shut it off at high speed. As was said by F_R those motors have 2 distinct carb systems.

Those leather seals are very important for the carb function so that it primes properly and doesn't leak fuel.
 
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Crosbyman

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Nov 5, 2006
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you may want to read up on the carb section in the johnson manual


here is the link just select the book stack….. then JOHNSON ….. then the Johnson red book and go to page 87 at boat info site

http://www.boatinfo.no/
 
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