MarkT; Yes, the problem began with a miss, but eventually it completely failed. In hindsight, I could have just rewound the source coil, but at the time I was not convinced it could be the real cause.

what ignition coil is it im looking for a replacment for mine also having elctrical issues think its a condenser but need coil due to somone cutting the wire to short
 

Nerdythrone567 if you just want to see if it sparks or want to start it up--if it does spark-- without any cost, you could unbolt the coil to get it close enough to the plug then just make simple steel bracket to support it & so it's earthed.
Give points a clean or at least a scratch so they contact--i can hear it running from here!!.

I thought 50 RPM would be more than enough to create a spark? How fast does a kick-starter turn the engine over?
The Fluke meter was on Min- Max.
I do own an O-scope, just not a high voltage probe. I can catch the the Source Coil pulse.
I've tried several new spark plugs that produce a blue spark on my stationary engine, but nothing on the Yamaha.

I'm pretty sure I suggested swapping ignition coil not spark plug.

MARKT you misunderstood my reply. I tried several new spark plugs. The ignition coil is brand new. The one I removed is also new by a diff owner. Both coils are producing the same Ohms and voltage out.
I just wanted to see if diff spark plug gap would produce any spark. No go.
As posted, I'm the 4 TH owner who has tried to get a spark. The other 3 gave up.
Not me.

Ok, just out of interest i did a test on my AT1 magneto model [now 175 but!!] which hasn't had the flywheel off for 30-40 years.
Took a pic of my sourcy thing which looks different to yours by memory, & also took a pic of the coarser windings lighting coil just because.
Spun it up disconnected from plug coil & with a plastic cable tie holding points open & got around 35AC volts at a good drill speed.
My small meter goes high enough but my old big yamaha meter only goes to 20 or so on AC & DC--but anyway!!.
So then i ran the motor with a slitpin in the coil connector &--forgot to write it down but i'll put up the videos i took & see if you can decipher them if clear enough.
Not easy to juggle everything.
Hang about i'll put the pic on g/photos & vids on youtube. Might take me a bit.
Yes dear i know were going out for dinner but this is important.

Here's spinning it up on 50 ac volts showing about 35volts--if you can see it.

Might be a bit of a jumble but hope they show.
One is a video that wouldn't take on youtube & not sure why it plays on google photos but anyway, shows my yamaha meter with a 20 volt limit on dc & ac volts.

photos.app.goo.gl/YfnkV3LTQUZBncwB6
photos.app.goo.gl/JoroPUBZiVFvaULT6
photos.app.goo.gl/zEdWkp97Nx73yyeq8
photos.app.goo.gl/Kt4ienYsJH8SeCSi6
photos.app.goo.gl/BAJeoRvCTqE9PVBq6
photos.app.goo.gl/WCQM88yuU9jgFdX68
photos.app.goo.gl/dgaNE5qhNq8HN1Np6
photos.app.goo.gl/d6v4pV4uXqNNsbR8A
 

RapidRob, you may have missed my point about so many people having issues with "brand new" coils being sold.  My advice (that you asked for) was I would try the coil on another points magneto or try a used but known good working coil. "New" doesn't mean "working".

RT325...  nice job...  wedging the points open makes good sense!  Not sure but the RPM but sounds more like 500 than 50.  It's late here and been a long day so I didn't get a chance to look at all the photos.  (I don't know if my old video editing computer still works but I have some sound editing software that I could use to measure the frequency of the sound peaks and possibly determine the RPM)