1993 40hp Johnson Starts for about 60 seconds and shuts off

Crosbyman

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Nov 5, 2006
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5,446
bluearo... when an engine dies it has lost fire (sparks) lost the fuel source or has lost a source of oxygen usually somthered by exhaust fumes sucked back in the carbs.

when your engine dies you must determine the cause to find a solution.

easyest when it does die is to just pull a plug, ground it to the engine frame and crank it over with the starter.... you should see strong sparks and if you do..... that means fuel became absent to keep the engine going.

You can have a fuel restriction anywhere from tank (poor venting) bad hose bad filtering dirty carb, air leak preventing sucking new fuel to the carb etc....

If you have NO SPARKS while cranking you have an electrical issue to solve.

Some components can react badly to engine heat and shut down or short out . Sometimes the application of a cooling spray will restore the function (sparks) till the heat builds up againg internally. At least that can help determine was is going on. To cool things fast I use an inverted keyboard spray can from the Dollar store.

hence the repeat question.... DO YOU HAVE SPARKS WHEN IT DIES !!
 
Last edited:

BlueAro

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Joined
Jun 6, 2023
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Sorry, I didn’t quite get the concept when you posted it. I understand now so I will check those items and see what I get. I truly appreciate you taking the time to clarify that. Thank you.
 

ct1762@gmail.com

Master Chief Petty Officer
Joined
Jan 17, 2019
Messages
859
Once again my comment about using the factory service manual went ignored. Keep struggling with it, or go through the proper procedures for troubleshooting and/or synch n link in the manual.
 

ct1762@gmail.com

Master Chief Petty Officer
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Messages
859
one of the easiest tests to see if its fuel or spark is to squirt premix into each carb at idle from a syringe or similar. if it increases rpm= fuel/running lean. if it pauses then dies, its not fuel.
 

BlueAro

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Jun 6, 2023
Messages
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Once again my comment about using the factory service manual went ignored. Keep struggling with it, or go through the proper procedures for troubleshooting and/or synch n link in the manual.
My apologies, I had missed that comment but got the manual and working on it now. Thank you for the tip.
 

BlueAro

Cadet
Joined
Jun 6, 2023
Messages
13
bluearo... when an engine dies it has lost fire (sparks) lost the fuel source or has lost a source of oxygen usually somthered by exhaust fumes sucked back in the carbs.

when your engine dies you must determine the cause to find a solution.

easyest when it does die is to just pull a plug, ground it to the engine frame and crank it over with the starter.... you should see strong sparks and if you do..... that means fuel became absent to keep the engine going.

You can have a fuel restriction anywhere from tank (poor venting) bad hose bad filtering dirty carb, air leak preventing sucking new fuel to the carb etc....

If you have NO SPARKS while cranking you have an electrical issue to solve.

Some components can react badly to engine heat and shut down or short out . Sometimes the application of a cooling spray will restore the function (sparks) till the heat builds up againg internally. At least that can help determine was is going on. To cool things fast I use an inverted keyboard spray can from the Dollar store.

hence the repeat question.... DO YOU HAVE SPARKS WHEN IT DIES !!
I bought a spark tester and was able to confirm that I have spark when it dies. Thank you
 

Crosbyman

Vice Admiral
Joined
Nov 5, 2006
Messages
5,446
time to focus on fuel issues.
looks like it can run a few initial drops of fuel then runs short (carb job should help)

otherwise the ignition is flaky...try coolant spray on ignion parts while runs and if it keep running longer the coolled part is suspect.
 

909

Chief Petty Officer
Joined
Jul 19, 2021
Messages
537
Bad carb cleaning.
You can't just clean a carb without the right equipment / materials.
 

oldboat1

Fleet Admiral
Joined
Apr 3, 2002
Messages
9,612
Early production carbs have a low speed orifice (jet) on top, and h.s. on the bowl bottom under a cover bolt. Both have to be squeaky clean. If you are not ready to rebuild the carb, carefully run a piece of weed whacker line through the jets, followed by a shot of carb cleaner using the plastic nozzle. The later production carbs have a plastic top and two or three jets -- same treatment would apply.

The point of measuring spark is to test magneto strength. It's done without plugs, using a device like yours (presumably) or a simple one like this:
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