Everything has to be right for the timing

So the new plug was in, and sure, she was trying to fire but she just wouldn't run.
I gingerly (i didnt want to strip any threads again) tightened things down in the attempt to ensure that there was no air leakage in or out of the barrel (weak fuel mix / low compression) but to no avail.
I checked the contact breaker points gap, and investigated the advance/retard timing.  A fellow Manurhin owner and regular rider (so therefore knows what he is talking about) had told me that the easiest thing to do was to rotate the stator plate hard to the left (anti-clockwise) - no timing adjustment required "it works for all versions" - but it wasnt working for me - so I spent a long time finely adjusting the timing - bearing in mind that each adjustment required the starter mechanism to be removed and refitted - it was all very boring - and nothing was helping my engine to run correctly.

Eventually I reasoned that my condenser was knackered, and having the spare engine from the old black donor Manurhin, I looked into exchanging the condensers (and perhaps the stator and flywheel)
I should have guessed..... it was never going to be that easy!

My flywheel on left,   donor bike flywheel on right

It turns out that I have 2 manurhin engines of different designs.  Which, while didn't help me resolve my problem, was interesting to discover and learn about.  I don't know for sure yet, but I think I am looking at the difference between what the spares manuals call "Polygone coupling - cone 1.75" and Polygone coupling cone BNA 15%" This has always baffled me - The exploded parts diagram shows the crankshaft with 2 part numbers and these two descriptions.  I need to strip the latest engine to investigate further but for now the 2 first obvious differences are 1. my engine has a pin dowl to position the flywheel on the crankshaft while the other engine has a woodruff key, and 2.  My engine has a far smaller diameter crankshaft than the other - which means I couldn't swap the flywheels even if I wanted to without swapping the crankshafts too.  This investigation; to be perused one day when my scooter is on the road and my bench is clear.

More importantly though, as I removed my flywheel from the shaft I found, to my horror, that the pathetic alignment dowl (that i had had machined especially) had sheered!
When had it sheered?... and then I started to wonder...... if the flywheel was out of alignment due to a sheered pin then maybe this is why the engine wasn't running correctly?
I wondered how the pin could have sheered - granted it is a pathetically thin pin - 2mm dia - and I had only used silver-steel for the pin (preferring this to be damaged if anything was going to be damaged - So actually this was a perfectly designed fail!) - but I wondered if I had tightened the flywheel onto the tapered shaft enough? The trouble with 'experimental' rebuilds (as opposed to a known rebuild) is you are always fitting and removing so sometimes don't do a proper tighten-up of nuts...... had I let the flywheel run loose?
Whatever the reason for the fail, I was motivated again to see if this was the simple solution to my running problem.  A quick drill out of the sheered pin, another pin made up, some careful refitting and lots of tightening, and....... bugger me, she started and ran like a dream!
I've said it before, and I'll say it again...... I am a nobhead! ;-)