84 Telstar starting problems

[Astaroth]

I've got a 1984 carburetted telstar ghia that's having some intermittent starting problems. Generally in the cold it has difficulty, when it's warm (e.g. above 5 degrees) it doesn't seem to struggle as much.

When the problem occurs, the car kicks over fine but will not fire. The (digital) tacho does not give any sign of life while it's kicking and it doesn't even struggle to fire. Battery voltage at full charge is 12.8v, with car idling is 13.6v, while cranking is 9.9v. We pulled plugs 1 and 3 out and kicked it with them on the head, and it threw a fairly weak but visible spark.

In a flash of brilliance I decided to short the ballast resistor to see whether the switching circuit or relay itself was stuffed. This turned out not to be too brilliant an idea - the wire from the resistor to the coil melted I fixed this up and removed the short, and everything works fine. It even started this morning

It's really starting to bug me and I'm in need of a bit of help. Was going to take her to the auto elec but I just thought I'd see if there's anything else I can try? I was going to swap in the coil from my pulsar to eliminate that, any other ideas?

Thanks!