Varitronic help

I'm trying to diagnose a fault on my mates Varitronic ignition system.
The scoot occasionally starts splutters then stops.
We tried all the usual stuff, cleaning and remaking connections, disconnected it from the ignition switch, checked and cleaned all the earths. Changed the suppressor cap, HT lead and plug We have a spark but it's poor.
Replaced the coil for a new one, the plug sparks but not well.
We changed the whole ignition system for a BGM and scoot starts and runs great so we know the rest of the engine is ok.
We stripped back the loom to try and identify if there was any mechanical damage to the wires and nothing visible.
Unfortunately I don't know how to test the stator or how it advances and retards the timing.
Can anyone help.
The scoot occasionally starts splutters then stops.
We tried all the usual stuff, cleaning and remaking connections, disconnected it from the ignition switch, checked and cleaned all the earths. Changed the suppressor cap, HT lead and plug We have a spark but it's poor.
Replaced the coil for a new one, the plug sparks but not well.
We changed the whole ignition system for a BGM and scoot starts and runs great so we know the rest of the engine is ok.
We stripped back the loom to try and identify if there was any mechanical damage to the wires and nothing visible.
Unfortunately I don't know how to test the stator or how it advances and retards the timing.
Can anyone help.