1989 Yamaha 20LG missing on #2 Cylinder

Cleco

Cadet
Joined
Oct 23, 2016
Messages
10
Hello,

I have a 1989 Yamaha 20HP outboard that I bought used and is basically brand new as it was never used, maybe several tanks of gas burned. I am having a problem with #2 cylinder misfiring. Here is what I have done so far:

Before I tried to start:

-Cleaned out tank and lines, changed fuel filter.
- installed new plugs (two sets)
-removed carbs cleaned them completely, they were not dirty at all.
- oiled cylinders

Tried starting, ran, but a bit rough. Took it out for a run on my boat ran ok for 15 minutes and then dropped cylinder.#2 cylinder misfiring, pull that plug cap and engine hardly changes, but pull #1 plug cap and it dies immediately.

Since then:

-checked plug caps and wires, they are like new. Ohms check on caps OK (replaced caps)
-swapped coils around and problem remained with #2 cylinder
- swapped out plugs
- tried different tank with known good one
- checked timing both #1 and #2, both good and advances and retards.
- checked both coils with meter
- removed flywheel and inspected charge coil and trigger coils, again like new and checked with meter....ohms checked good
- rebuilt fuel pump, no change.
- removed carbs and cleaned again. Still no dirt
- checked all wiring connections all good. Cleaned up every ground I could see.
- removed flywheel again and swapped trigger coils around, no change.
-

This leads me to believe that the CDI box may be buggered..Can not find a CDI anywhere.

Added a few pics to show that this engine is like new and not a worn out piece of junk...lol

Please help as I am stumped.
 

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mjf55

Chief Petty Officer
Joined
Jun 17, 2014
Messages
462
Spark, fuel, compression
You did a lot to test spark and fuel. What are the compression numbers for each cylinder?

EDIT: I see you are focused in on the flywheel / rotor in your other thread as the potential issue for your no / weak spark. You should combine them to one thread.

Cannot help on those round portions on the hub of the flywheel as to being magnetic or not.

BTW, the G in LG indicates a 1988 motor.. Did not see a 20hp listed in parts listings, just 25.
 
Last edited:

Cleco

Cadet
Joined
Oct 23, 2016
Messages
10
20161014_151650.jpg
Spark, fuel, compression
You did a lot to test spark and fuel. What are the compression numbers for each cylinder?

EDIT: I see you are focused in on the flywheel / rotor in your other thread as the potential issue for your no / weak spark. You should combine them to one thread.

Cannot help on those round portions on the hub of the flywheel as to being magnetic or not.

BTW, the G in LG indicates a 1988 motor.. Did not see a 20hp listed in parts listings, just 25.

My mistake on the year..... you are correct it is 1988...wrote it down wrong

Did compression test, 120 psi both cylinder's

Trying to figure out how to edit original post to reflect year and compression.

Don't know what to say about parts listings, it is a 20hp

See attached pic of ID tag.

Thanks
 
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