Yamaha F20 no spark.

[telstar1]

2014 f20 yamaha. Spark very weak,you can feel it and a faint spark will jump from a screwdriver in sparkplug lead,to ground,but it won't jump the plug gap. Checked temp sender and lanyard switch both ok.I have an 8 hp that has I blvd a similar coil so am going to swap but I doubt it's that simple.
I don't have a manual so that's a hindrance. Any link to one? I'm thinking the evidence suggests it's the CDI module but don't know how to prove it.
Suggestions welcome.

 

[boscoe99]

CDI output is based on CDI input.

How is the input to the CDI?

www.yamahapubs.com

 

[telstar1]

CDI output is based on CDI input.

How is the input to the CDI?

www.yamahapubs.com

CDI output is based on CDI input.

How is the input to the CDI?

www.yamahapubs.com

Don't know.im at a distinct disadvantage having no manual. I'm thinking the CDI gets its input from the pulser coil? So it could be a weak pulser coil maybe. The one on the 8 hp looks similar enough maybe I should give that a shot.
I swapped the main coils with no joy.
Interestingly even with a practically non-existent spark the engine will run for a couple of seconds when it's cold

 

[boscoe99]

CDI unit gets its input from the charge coil. It "charges" a capacitor within the CDI unit. The pulser coil tells the CDI unit when to discharge electrical power to the ignition coil.

www.yamahapubs.com

 

[99yam40]

if it fires and runs when cold,
I would think you have a fuel to air mixture ratio problem or timing problem maybe.
but it is best to test everything you can and then chase what you cannot test

 

[telstar1]

So the charge coil would be the generator under the flywheel I m guessing?

 

[99yam40]

So the charge coil would be the generator under the flywheel I m guessing?

yes they are some of the coils under the flywheel.
so are the pulsar coils
there are also lighting coils under there that create the power to charge the battery