So, found this guide on engine tuning...

Ignition occurs when the magnetic field colapses from the primary windings, when it is switched off....the points opening....and the condencer is collecting back EMF ( electro-magnetic force)....approx 300 to 400V.....then the secondary windings build up and lets go the spark the lights the fire.
Roughly as an example....primary winding has 200 coils of wire, the secondary will have 20,000 coils of wire.
When you replace points, replace the condencer too...this helps stop the points burning.
A good idea is to run an earth wire from the dizzy housing to the battery - terminal.....need a good earth for the dizzy.
Another thing to check is for vacuum leaks at the carby base gasket and intake gaskets...loose nuts/bolts at either.....and split vac hoses too.
Check condition of other ignition components too.