Thanks rebuilder86, I did check that the engine was earthed i.e. checked it wasn't loose and looked undamaged, no electrical test though. The engine cranks so I would assume the earth is OK.
So far we have replaced :
- Coil
- Ignition leads
- Dizzy cap
- Rotor button
- Points
Checked :
- Battery Voltage (12.4V)
- Voltage at the ballast resistor (12.xV)
- Voltage the coil + (10.xV)
The 15 amp "engine" fuse looks solid but one of the end caps is loose.