Johnson 2 hp Carb problem??

[JohnRude]

My first motor. I’m new to this. My 1974 Johnson 2hp has great compression and spark. It starts and runs OK but at low speed the choke has to be on full or it dies. At high speed it runs fine with the choke all the way in. It just won’t idle without full choke. What did I do wrong? New mag parts and cleaned the carb. New plug. Fresh fuel. New impeller. I don’t want to scrap it.

 

[crosbyman]

if crankcase  vacum to pull in the fuel fumes is ok then the fuel is not being  extracted from the upper low speed circuit.

there is a very small side openning  in the  upper half of the carb  that sends fuel  up into a drip chamber.      it  needs to be open an clean

packing of the LS needles may be  faulty  allowing air to be drawn in .

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• This reply was modified 2 years, 11 months ago by crosbyman.
• This reply was modified 2 years, 11 months ago by crosbyman.

[billw]

Define “great compression.” Those engines will run, albeit poorly, with less than stellar compression. Ideally, compression should be 100 or up.

That being said, odds are you did miss something in the carb cleaning and/or reassembly. Did you try adjusting the low speed needle more outward? (These engines take awhile to dial in the low speed adjustment, with some patience.) Did you use new packing for the mixture adjustment screws? Did you use a new main nozzle gasket between the upper and lower halves? Did the mixture adjustment screws turn with your finger tips before you tightened down the packing nuts? Does your low speed mixture needle have a good point on it? Is the float installed correctly and not upside down? (It is possible to do.) Did you use compressed air to blow out all passages? Does the throttle plate move freely? The side passage Crosbyman mentioned is the main low speed part of the carb. Using a WD 40 can with the red spray tube, blow into all those passages and make sure they are clear. I would take your carb apart again and check thsee things out. If it starts easily, that is a good sign that the engine is not junk.

Long live American manufacturing!

• This reply was modified 2 years, 11 months ago by billw.
• This reply was modified 2 years, 11 months ago by billw.

[JohnRude]

Thanks. Well, the compression is 95 psi so I hope that is positive. Your remarks make sense and it’s fairly easy to go through it. It was my first carb rebuild. Doing it again would be good practice. Crosbyman mentioned crankcase pressure….the last great mystery. How do I check that? I don’t want to give up on this patient. It even has new paint and decals.

[JohnRude]

Thanks Crosbyman. Not sure how to check crank pressure and I was told by someone to never remove that aluminum plug. I know they come in a carb kit.

Your leads helped last time getting an Evinrude 7518 running. This gives me something to go on.

[crosbyman]

easy stuff first…  side channel clean-out   with carb cleaner… blow dry

with the carb body seperated    remove the ls needle and  blow carb cleaner  in the LS  circuit towards the  upper LS chamber     see in the above pict.

Do this while  blocking the side channel with your finger to keep the spray flowing towards the front chamber

at one point you should see that carb cleaner solvent come out of the 3-4 small holes  indicationg  regulat fuel would flow also.

 

see minute 16:45  in this video

(1571) 1971 2 hp Johnson Mate – Stalls at WOT – Gets a Carb Clean. – YouTube

If not the holes (chamber)are/is clogged.   nothing  wrong/difficult  with removingt the dime size plug with a pick…. after drilling a small hole in the center …(NOT TO DEEP !!!)

Inspect…  clean…  blow  all the LS circuit route . Install needle  but do not close it.  spray carb cleaner again up the side channel  and it will exit into the chamber via the very small hole in the side wall of the chamber  ….     blow dry

reinstall a new plug on top and  punch the  center a bit to expand the perimiter and seal the  edges.   I apply  fingernail polish around the  edges  to seal it

see  videos on a 9.5 carb…not your 2hp  but  same  basic principle            see part#1 at 5:10 minutes for the dime size plug process

 

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwjk0-yq0vD3AhVekYkEHfZGAygQ3yx6BAgDEAI&url=https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3Dr-VTkOuSg00&usg=AOvVaw1Ht2ZzUe6jaUo8p34Xa17n

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwjk0-yq0vD3AhVekYkEHfZGAygQuAJ6BAgEEAU&url=https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DY2pwU5aho9U&usg=AOvVaw1f2ScHZU7JXy5P7GIcFy1P

 

 

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• This reply was modified 2 years, 11 months ago by crosbyman.
• This reply was modified 2 years, 11 months ago by crosbyman.

[fleetwin]

Is this engine new to you?  If not, did it ever idle properly?  You mention having the carb apart, was it real dirty inside when you had it apart?  Like Bill said, I’m hoping this engine is OK internally.  You mention it starts well and performs well at full RPM, so that is encouraging.  The 90PSI compression reading is probably “OK”, compression gages are often inaccurate on engines with small crankcases like this one.    You also mention that the engine will idle with the choke partially engaged, another good sign.

So, let’s start at the beginning with the carburetor.  These engines have no lower cover, so the throttle linkage is exposed to all the elements, especially in salt water.  Has this engine seen salt water use?  If so, the carb throttle shaft may be binding/stuck, so the butterfly might not be closing fully.  The only way to properly determine this is to remove the carb and have a look in the back of the throat to make sure the butterfly and shaft move freely and has sufficient spring pressure so the butterfly closes completely on its own when the carb is off the engine.  This engine will not idle properly if the butterfly does not close completely and easily at idle.  The next thing to look at is the throttle plate/ignition cam on the mag plate to make sure it is properly adjusted, you will see that one end of the cam is slotted where the attaching screw goes through.  Did you mess with that at all?  In other words, if someone inadvertently messed with that adjustment, perhaps the cam is holding the throttle plate open slightly at idle.  Needless to say, this adjustment can only be checked with the carb installed on the engine.  There are two little scribe marks on that cam, which is where the throttle plate should just start to open.  Feel free to post pictures here, good pictures are worth much more than my words, and will help us evaluate and explain things for you.   D

[crosbyman]

btw my brother was gifted  one of these 2hp by his then girl friend  …long ago.

He always  cursed at it for not running properly.  Turns out the carb had a small crack in it.

Brother passed away few years back, I think the 2hp is still in  his  widow’s  shed  .

He never married  the girlfriend who  gave him the motor ….   How could a guy not marry a woman who gives you  an outboard… maybe it was the  2hp’s fault.

 

She should  have gone  with a nice  JW 🙂

 

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[Mumbles]

I wouldn’t advise drilling a hole in the Welch plug unless you use a drill press. One small slip with a hand held drill and you’ll be looking for a new carburetor.

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