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Johnson 35 running but not for long

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Hubertcj

New member
So I'm having a new issue with my 1978 Johnson 35hp outboard. I run it in the driveway hooked up to the hose and it seems to run ok. Then I take it to the lake and am able to get it running full speed at 25mph for about a minute, then it cuts off and won't run above idle again. Was able to get it back to the dock at idle speed but any more and it cuts out. Also plug seems to be fouling as well.

Any ideas?

Thanks in advance!
 
Has it ever been overheated? Any discolored paint on the cylinder head or exhaust cover? They had a serious cooling problem about that time.
 
So took it out again today with fresh plugs. It runs great for a few minutes and then won't run above idle. If I push the throttle, it cuts out. Also if I push the choke in it gets a little better. Got a local guy with a carb so I'm going to try swapping carbs tomorrow. Runs beautifully at idle no problems at all.
 
Hubertcj said:
So took it out again today with fresh plugs. It runs great for a few minutes and then won't run above idle. If I push the throttle, it cuts out. Also if I push the choke in it gets a little better. Got a local guy with a carb so I'm going to try swapping carbs tomorrow. Runs beautifully at idle no problems at all.
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Sound like high speed circuit clogged or gasket that goes around the high speed tube that gets sandwhiched bewtween bowl and carb body could be bad.Just had that issue with gasket on a motor.Bogs at full throttle,but it did bog right away not after a minute.
 
If you can find the throttle cam lever, watch what it does when you shift from neutral to forward, and back to neutral. (Doesn't need to be running)<br>The roller on the throttle cam lever should still be touching the spark advance lever after you return to neutral. Or, be really, really close to touching.<br>The throttle lever is item #34 on this diagram:<br><a data-cke-saved-href="https://www.marineengine.com/parts/johnson-evinrude-parts.php?year=1978&hp=35&model=35EL78R&manufacturer=Johnson&section=Magneto" href="https://www.marineengine.com/parts/johnson-evinrude-parts.php?year=1978&hp=35&model=35EL78R&manufacturer=Johnson&section=Magneto">https://www.marineengine.com/parts/johnson-evinrude-parts.php?year=1978&hp=35&model=35EL78R&manufacturer=Johnson&section=Magneto</a><br>
 
Hubertcj said:
So took it out again today with fresh plugs. It runs great for a few minutes and then won't run above idle. If I push the throttle, it cuts out. Also if I push the choke in it gets a little better. Got a local guy with a carb so I'm going to try swapping carbs tomorrow. Runs beautifully at idle no problems at all.
Click to expand...

The symptoms you describe suggest a problem with fuel flow or delivery

Check the fuel tank vent ( Take the cap off , but don't lose it)

Air ingress into fuel line. Prime suspect is the O ring in one of the fuel line connectors Try pumping the fuel line bulb as suggested earlier.

Defective fuel pump. Pumping the fuel line bulb will overcome this too.

Restricted fuel filter

Restricted fuel inlet to carb or needle valve or float sticking.

It is unlikely to be clogged passages or jets in the carb because it idles Ok and runs " great" for a few minutes

Do some diagnostic investigation before going as far as swapping the carb for another ....... you don't want to introduce any complications
 
Thanks everyone for the help. Traced the fuel system through looking for issues, really couldn't find anything. Took the carb off and cleaned thoroughly and then used compressed air to finish and dry. Ran perfect for 3 hours today with absolutely no problems at all. Also picked up a stainless prop and got an extra 3mph too end. I really appreciate all the advice and am thankful to have a community like this where we can help each other. Thanks again!
 
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