I've got a S2 bluebird electronic distributor in the A15 and of late when starting from cold it just loses spark even if holding idle at 2000rpm it just dies. I was watching the spark today with the lead pulled back and as it stutters you can see there is no spark. Soon as it warms up this problem seems to disappear. Also you can see the tacho bounce when its playing up.

Im wondering is it possibly the ignition module is dodgy or the guts of the distributor?

have you checked the spark plug and coil leads?

Spark is strong when its there. Hold the lead back from the plug and you can see it jumping and you can also see it stop jumping as it stutters.

The module in the dizzy may be shot. Take the dizzy to an auto sparky to test it on the test bench. Ask him to record the advance curve while it there. Could be handy for later