OK tried the strobe light on both my bikes, same for both magneto and electronic, works fine if you have the arrow pointing towards the plug , absolute Zilch if facing the other way.
Further little bit of info that might help someone someday, the strobe light is a Draper - 12 volt but works on 6 volt fine allowing that the light is not so bright but would be good enough to highlight you timing mark.
Just thought I'd mention both started first kick, Flash settled down to a nice even tickover (of course) RGF needs a good bit of wrist action to keep going until it warms up - still of the opinion it needs to be richer, shed refurb 99.9% there so maybe this week I'll get at it