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1989 Johnson 20hp carb adjustment

Jupiter Dinghy

Jupiter Dinghy

Regular Contributor
As I am waiting for the manual to arrive, couple of questions:

First question, Do these motors come with no air box in front of the carb (as in the 9.9/15hp)?
My first reaction when I lifted the cover was to think the air box was missing! lol

Secondly and as per the post title, would someone be able to kindly indicate how carb adjustments are done on this puppy?
(Idle & fuel/air mixture mostly), is the fuel/air ratio adjusted with the screw at top center of carb (as in the 9.9/15hp)?

Gracias! Merci! Thank you!
 
It hasn't run in years, started after a 2 or 3 pulls though, but lotsa smoke and after I let it run at a high idle, it eventually farts (or coughs) and stalls.
Starts right back up, so I thought the carb needed a rebuild maybe? Unless a cleaning would do? Problem is I need to replace those damn core plugs that you have to pull after punching a hole in them to clean all the airways... that's why I was thinking about getting the kit as they come with it.
 
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Just screw a sheet metal screw in th soft plugs and pop them out. Remove everything except the butterfly and soak overnight in carb cleaner. Blast the corcuits with high pressure water and blow dry with compressed air. Use a socket half the width of the soft plug and gently tap it clpse to flat i use loctite to seal the edges. Only use the weight of tfloat to check float is level pull the float to adjust it never use finger pressure on the float. I wouldhet some gasket material and make a gasket that matches the flange on your carb with the correct hole size. I also lightly surface the flange on a glass table with 220 grit only pull the carb in one direction until it all sninesthe same pull the carb down slow and even to nice and snug do mot overtighten. Check adjust sync between spark advance and throttle opening. The butterfly should just begin to open as the mark on the cam passes center of the follower roller.
 
(Carburetor Adjustment - Single S/S Adjustable Needle Valve)
(J. Reeves)

Initial setting is: Slow speed = seat gently, then open 1-1/2 turns.

Start engine and set the rpms to where it just stays running. In segments of 1/8 turns, start to turn the S/S needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running.

Eventually you'll hit the point where the engine wants to die out or it will spit back (sounds like a mild backfire). At that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.

When you have finished the above adjustment, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.
 
Thanks folks!
kimcrwbr1: About soaking the carb body in carb cleaner overnight..... is there a way I can get carb cleaner in the liquid form somewhere, other than in a spray can, so I can pour it in a container for this purpose? Or what kinda liquid do you recommend?
 
Sounds like a plan thanks.
Letting it soak in highly concentrated degreaser such as this one, basically right?
Or should I go more like acetone?

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If that motor started after years of sitting with 2 or 3 pulls there likely is no need to " rebuild " the carburetor.----Adjust it and go boating.
 
racerone said:
If that motor started after years of sitting with 2 or 3 pulls there likely is no need to " rebuild " the carburetor.----Adjust it and go boating.
Click to expand...

I love the sound of that, but the coughing and stalling at idle isn't too inviting for a run on the water..... will give adjustment a shot later today though, I haven't touched the slow speed needle yet.
 
NOTE: Clean the high speed jet located horizontally in the bottom center of the float chamber, way in back of the drain screw, with a piece of single strand steel wire as solvent just doesn't do that job perfectly.

The carburetor cleaner Kim spoke of....... I bought one of those years ago... looks like a one gallon can, comes with a basket for small parts, contains regular heavy duty carburetor cleaner, same stuff as the bigger 5 gal commercial containers.

Back then, it was $10... later in years, I noticed it was $20, what it cost now is ???
 
The motor may not have a warning system or overheat shutdown features.-----A wise man would install a new impeller before launching the boat.
 
Thanks Joe, will stop at the auto part store after work for this carb cleaning kit basket...
Racer: I already ordered the impeller, (man, I'm wise!) but the motor temp was fine, I measured 125 at the head, steady on each cyl. after warm up.
Compression readings were about 110 on each. This motor sounds healthy, I just think it needs a carb job. Hopefully.
Any recommendation based on experience between the Champion plug and the NGK equivalent? (I always used NGK on my 9.9's as they were recommended by the famous Leroy's ramblings)
 
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joereeves said:
Back then, it was $10... later in years, I noticed it was $20, what it cost now is ???
Click to expand...

$30.
Guess it goes up by $10 increments... lol
So the hell with that, I bought 2 extra spray cans of carb cleaner for $2 a pop, and I will empty them in my homemade "dip tray"..... and I'm sure the carb will be as happy with the soak as it would have been in the $30 can. :)
 
Price increases like that soon put a business...... out of business!

Yep, a few $2.00 containers and a coffee can will do the job nicely.
 
joereeves said:
Price increases like that soon put a business...... out of business!
Click to expand...
You got that right Joe.
Incidentally, I started the motor again tonight, and it ran excellent, including idling nicely...... until I pushed the choke all the way out, and then it started coughing and stalled. So as long as I leave a bit of choke, it runs perfectly, what does this mean?
 
Possible vacuum leak just do the rebuild and give it good sync after you mount the carb. Yoi can get it exact by fastening straight paperclip or stiff wire to a alligator clip and fasten it to the throttle shaft on the carb that tells you exactly when the butterfly begins to open.
 
Oh! And while I have your attention..... Procedure to remove lower unit on that thing is the same as on the 9.9/15hp right?
Open a gap at the mid section to unscrew the gear shaft link and pull out?
 
Jupiter Dinghy said:
You got that right Joe.
Incidentally, I started the motor again tonight, and it ran excellent, including idling nicely...... until I pushed the choke all the way out, and then it started coughing and stalled. So as long as I leave a bit of choke, it runs perfectly, what does this mean?
Click to expand...

Clogged, restricted carburetor... fuel not flowing as it should. Clean and adjust as advised.
 
Looks like someone hacked it for some reason? Blast out all the corcuits after the soak and install the soft plugs. Do you have the correct plugs in the kit?
 
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