Home › Forum › Ask A Member › 1962 18hp Johnson Only Runs With Choke.
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fleetwin.
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September 6, 2016 at 4:20 pm #5184
My 18hp Johnson is not cooperating with me. Maybe you guys can help me out. I replaced coils, plugs & wires, points, water pump, fuel pump and lines, and cleaned & rebuilt the carb. It only runs with the choke. I have an air leak somewhere. I’m thinking crank seals. Any ideas? The tank and fuel line are new. Thanks, Mark
September 6, 2016 at 5:15 pm #43449OK Mark, well let’s not go nuts changing seals just yet….
I would have a much closer look at that carb first…Was the carb gummed up when you rebuilt it? I’m assuming this carb has an adjustable high speed needle, not a fixed high speed jet, am I correct?
Where do you have the needles set at?
The low speed needle (top) is initially set at 1.5 turns out from gently seated
The high speed needle (bottom) is initially set at 3/4 turns out from gently seated
Are you sure the low speed needle tip is not damaged, perhaps broke off and stuck in the mixing pocket holeSeptember 6, 2016 at 5:20 pm #43450I’d look into the carb again. I suspect the low speed idle passage from the bottom of the bowl, up the side of the carb, or a clog from the low speed needle adjustment to the top of the carb throat is clogged. May also have a hardened clog at the bottom of the carb bowl where the high speed venture picks up gas. If the clog is just in the idle circuit it will run OK if you can get it going fast. Get a spray can of carb cleaner with the small tube and spray well through all passages. I sprayed for about a minute through the idle passage on the side of the carb bowl on my ’59 35 Evinrude until hard clog pieces started coming out, even though cleaner was coming through – then it ran without the choke. I too had to go into the carb a second time to cure this.
DaveSeptember 6, 2016 at 6:16 pm #43457Here’s a little background on the engine. It sat in storage for maybe 30 years. I bought it from the son-in-law after the owner passed away. The motor was winterized before going into storage. The carb had a little hard varnish on the bottom of the bowl and the needle and seat were stuck. Everything else looked surprisingly clean. I pulled the soft plug and it was clean inside. I sprayed carb cleaner throughout all the passages that I could find. Adjusting the low speed needle while running on the choke had an effect on how the engine ran. Low speed needle is set to 1.5 turns out. High speed is set to 3/4 out. I thought about the seals because it sat so long, but I guess I should pull the carb and see if I missed something before diving in further.
September 6, 2016 at 6:19 pm #43458Oh, I forgot to mention that the engine would only run when the choke was barley open, maybe a 1/16" between the butterfly and the carb throat. Full choke would cause it to die.
September 6, 2016 at 6:30 pm #43459When you say you rebuilt the carburetor, did you install a new OMC/BRP carb repair kit? Did you install the small seal between the carb top and bottom? It is a small round ring and it seals the inside of the bowl so no air leaks. It goes on the main nozzle pickup tube. If you used the old gaskets and such, it might be causing the problems you describe.
September 6, 2016 at 6:55 pm #43460quote rickrodt:When you say you rebuilt the carburetor, did you install a new OMC/BRP carb repair kit? Did you install the small seal between the carb top and bottom? It is a small round ring and it seals the inside of the bowl so no air leaks. It goes on the main nozzle pickup tube. If you used the old gaskets and such, it might be causing the problems you describe.My experience has been that if that small donut seal is missing or bad, the carb floods when you open the throttle above idle – the opposite problem of needing the choke on.
DaveSeptember 6, 2016 at 7:02 pm #43462A friend of mine had this same problem, he checked everything with no help. Then he found fuel line to carb. collapsed, new line fixed the problem.
September 6, 2016 at 9:19 pm #43471Yes, I used the new o-ring/donut that seals between the bowl and the top of the carb body. So, how common is it that crank seals go bad? I get the feeling that it isn’t very common. I have found very little information on how to do it, which suggests that it doesn’t need done very often. I’ll have to break into the carburetor again and see if I missed anything. I am partial to the new 4 strokes, but my wallet is not so I don’t want to give up on this motor quite yet. It is in very good condition, better than most I see. But, if it doesn’t run, it doesn’t do me any good. Also, I read somewhere that stuck open reeds can cause this issue. I inspected my reeds when the carb was off and made sure they weren’t stuck. One of them appeared that it may be slightly stuck open, like barely able to tell. If you have bad eyes you wouldn’t notice it was open. Could this cause the problem? I figured it would clear itself up after running it a bit.
September 7, 2016 at 3:40 am #43510I think I found the problem. I took the carb apart this evening and looked over all the passages closely. Low and behold, I missed one. I am so happy to have found my error. Another problem I gave myself was reversing the low and high needle settings. I just realized that the high needle is on the top and the low side is on the bottom. That makes sense. After looking back over the carb, the blocked passage is the idle circuit passage at the bottom of the bowl. I hope to give it another test run in the next day or two. I will let you all know how it turns out. I thank everyone who helped for keeping my focus on the carburetor.
P.S.
I inspected the reed valves again and they all looked as they should. -
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