Modern Vespa

No need to pull the loom. The only wire relevant to the ignition is the green one from the CDI to the kill switch. It should be obvious to tell the two green wires apart. A continuity tester or a multi-meter would show if there is a short in that green "kill" wire. It could be an intermittent short and running with that wire disconnected from the CDI would answer that question. Just kill the motor another way.

I'm going to fit a know good stator I will only run the scooter with the wires to the cdi green white and red
I will disconnect 2nd green to kill switch and the blue and black to the regulator
If I run it hard for a while see if the stalling issue returns 😬

If there was short in the kill wire, it would just cut the ignition, not cause the stator to load up so much that it "burnt out". I think that's right?

Without going back through your replies again SeanL, is it just the black pickup that fails?
If it is then checking power out of the stator to ground is probably a waste of time.

The feeder coil generates power and when shorted to ground ("killed") just generates power to ground. There is nothing that could back-feed it and "over power" it. The CDI could, however, be over-powered and damaged but I am sure it is designed to handle whatever the feeder ( unregulated) can produce. Otherwise they'd be crapping out all the time.
The trigger coil sits above the power coils and just senses the over-lapping magnets (you can see them on the FW) which triggers a capacitor circuit in the CDI to collapse the HT coil ( like points do) and fire the plug. Capacitor Discharge Ignition. My rudimentary understanding...

Are you running BGM stators? Known issue that they burn themselves up.

None of them BGM first is piaggio the other 2 are probably Indian copies

I'm not sure if it's the pick-up or low tens coil that's failing
Do the ohm readings I posted indicate which part is failing ?

Yes. Green to white resistance values show the coil or wiring being the problem.

Red to white show the pickup/ wiring.

White to ground show a ground wire problem.

I noticed that when the stator starts to fail it begins with the engine stalling at tick over for instance clutch in throttle closed coming to stop at junction
Does that help?

Plug chops when things are good and bad let's see

Thank you which of the readings are out of tolerance ?
And therefore indicate which part of the stator is failing

Here's some good values. Yours should be close to these.

White wire to engine case: .000 ohms
Red to white wire: 111.9 ohms
Green to white wire: 442 ohms

Please report back what you find. Anything drastically different than the above will point out the culprit

That would happen if it was running far too rich for some reason.
If it only stalls in that scenario, throttle closed, clutch in, I wouldn't necessarily suspect the ignition circuit.

I experienced this exact same problem when I built the 180SS and used an expensive brown bakelite ignition coil. Drove me nuts. Swapped in a basic generic coil and have never had the problem since. A CDI is just an ignition coil (the round part) that is electronically triggered by a capacitor circuit (the square part) instead of mechanical points. It can fail. A stator coil only generates power. The CDI has to deal with it.

OP
SeanL
30 May 2025 at 22:07
details
linkflageditquote
Stator readings ohm set at 2000
Stator 1 green to E 468, green to red 578 red to E 111
Stator 2 green to E 510 red to green 622 red to E113
Stator 3 green to E513 green to red 608 red to E 96
Are they ok or knackard what should the readings be ?

Should run with those. Which is the original?

All those look good. What about W to earth?

Any of the terminals crimped on? Are they tight and clean? Wiggle them and anything change?