No spark

I have the fuel system working now- I hope. However I have a problem with the ignition system. I renewed the leads and dizzy cap, the dizzy has been without a cap on for seven years, so it is looking a bit mouldy inside. I've cleaned it up as best I can without stripping the whole dizzy.

I have taken one of the spark plugs out, laid it on the block and cranked the engine. I get a spark on first switching the ignition on and again when I turn it off. Absolutely nothing when the engine is cranking though, what should I be looking at please to fault find?

Sounds like the Hall effect module in the dizzy is dead. Could equally be the wiring to the hall sender or the coil or the thyristor. Could also be the coil breaking down under current load.

I'll check the Hall effect IC and replace if it's duff, they are about £3, thanks for suggestion.  Whereabouts is this thyristor, is it in the coil?.. I'm toying with the idea of replacing with a conventional dizzy and coil

The thing in the scuttle on the heat sink

Mmmmm, too many connections to just be a thyristor, If it is that, I'm doomed