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Charles, Marine Mechanic
Category: Boat
Satisfied Customers: 3709
Experience:  US Navy (Ret) Certified Mercury Marine Tech with over a decade of repair experience.
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I have a Yamaha 1985 40HP 40ETLK outboard engine that is having

Customer Question

I have a Yamaha 1985 40HP 40ETLK outboard engine that is having some issues.
Submitted: 2 years ago.
Category: Boat
Customer: replied 2 years ago.
The issue with the engine is it will run fine for about 1-2min then it will completely cut out. It will start right back up but will not run very rough and only at low rpm. If you try to run at higher rpm it will cut out.
Customer: replied 2 years ago.
One more symptom is the trim is really slow when engine is running. However it works fine when its not running.
Expert:  Charles replied 2 years ago.
Hello, my name is***** you for allowing me to assist you today.
Do you know the engine voltage when it is running?
Has a compression test been done?
Customer: replied 2 years ago.
Compression is very good and within 8psi of each other. The engine can run perfectly sometimes and has as much power as an engine should. It just seems to start flaking out when it gets warm.
Not sure of engine voltage when running. What is the best way to test this?
Expert:  Charles replied 2 years ago.
Use a multimeter directly on the battery cables at the engine is the best way.
What all have the shops done to the engine and tested?
Customer: replied 2 years ago.
The one shop we sent it to said one coil pack seemed week and was replaced. They could not find anything else wrong with it. This was the beginning of last year though. This year the carbs were cleaned as well as stator, charge and lightning coil replaced.
Expert:  Charles replied 2 years ago.
Do they do any testing or just start to replace the parts?
how is the fuel system?
Customer: replied 2 years ago.
I think they just replaced parts. Motor has new fuel pump, cleaned filter, new fuel tank and oem line and ball pump, all new fuel lines and clamps. Could it be the CDI?
Expert:  Charles replied 2 years ago.
Heck, That is the only original part left. do you have a god multimeter, we can test it.
Customer: replied 2 years ago.
I do have a good multimeter can this be bench tested or do I have to test it with it on the engine?
Expert:  Charles replied 2 years ago.
We will test the input and the output from it. If the input is good and the output is bad. It is the CDI that is the bad part.
Expert:  Charles replied 2 years ago.
With the CDI still on the engine, Disconnect the brown and blue coming from the stator/ Measure the resistance between them. It should be 180-250. Then test the cranking voltage from these wires. Set the meter to AC and crank it over. the meter should show a peak reading of at least 175V.
Next unplug the wires from the pulser coils. There will be a white/red, a white/green and a white/black. Along with a black. Test the resistance between the whites wires to the black. All readings should be 310-390. Then do the cranking voltage on each white to black. That should be over 4V on each.
Plug everything back on if all of the readings are good. Crank over the engine or have it running and test the voltage going to the coils. If it is not at least 135V It is the CDI that is bad.
Let me know what you find.
Customer: replied 2 years ago.
Will do. Thanks!
Expert:  Charles replied 2 years ago.
Your very welcome. Please let me know what you find out.

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