Modern Vespa

So, she pulls up tonight and the engine dies just as she gets home. Lights were on but not very bright at all. Battery shows 10v

Fault clearly not fixed and as a reminder battery is brand new, parasitic draw shows 0.00 so no issues.

When engine running correct voltage going into battery even with lights on full beam.

I'm at a loss

Hoping it's the regulator, meaning it works for a bit then dies but is that even possible?

If not that then I just don't see what else it can be?.......

It could easily be that once it heats up the windings in your stator are breaking down. Heat in wiring and electrical components increases resistance. Have you run the voltage tests after the engine has been running a while and is essentially hot?

If as I also suspect, when hot battery not receiving charge, I'm assuming no way to know if stator or regulator at fault without swapping one to see then trying the other?

Is changing stator achievable without dropping engine out or is it a pain to do?

The really weird thing is I think there is a slight drain when not being used but according to multi meter, 0.00 parasitic drain..... But big issue is how when using it drains fast giving a dead battery within 20 miles

Had planned to do the hot run test today so will see how that goes.

I just had my similar issue resolved. All my tests said the strator was good and so was the voltage regulator. I was on my second brand new battery that I had to keep on a battery tender just to ride 10-20 miles. After giving up and taking it to a shop, they found a bad connector and shorted out wire in the wiring harness from the strator to the voltage regulator. They replaced all the wires and connectors with heavier duty versions and all has been perfect since.

So-please check that wiring harness for any insulation cuts etc. Your symptoms sound identical to mine. Check the wiring harness-I did, but missed the spot that was causing the short. And all those meter readings looked good when I was checking too. Good luck.

Thank you for the heads up.

I didn't get to do a hot run test today as when I started it this morning the meter only read 12.2v with engine running at idle and at revs.

Bought a used but genuine regulator (the one I bought last year for it was a new but Chinese one) last night on eBay as only £9 to try that so while fitting that I will also check the wiring in the front as well.

The weird thing is last time I checked the voltage while running was right so not sure if the regulator just goes or can be intermittent then go.

All I can do is in this order:
1. Replace regulator
2. Check wiring in front while apart
3. If still faulty assume it's the stator
4..... Having checked the above and still not resolved swear a lot, kick the bike, applogise to the bike for kicking it, tell the wife she needs to buy a new bike, then back to trying to find the issue :/

I also got the intermittent good readings on my voltmeter. Found that the wiring would move enough NOT to cause the short and everything was sweet, but it would short out when running and the vibration moved the chaffed wire in contact with the metal body causing the short. Crazy Gremlin and I cussed and kicked mine enough for the both of us.

Up to now you have failed to mention the " new but Chinese " regulator installed last year.

That would be my first recommendation to change out.

If you want good advice from people you need to give them as much information as possible. A non -genuine Chinese regulator is significant in this story.

Good luck with the replacement (although if the problem persists with the new but second hand regulator I'd still suggest replacing it again with an actual new one.

Where was yours chaffing?

It's been perfect for a year but we live & learn I guess... New to Vespas

At the back of the wiring harness just under the pet carrier. It was hard to notice by just a quick inspection, but after a more detailed look, you could see the insulation rub right where the wire went into the plastic plug. It was very, very small cut. I missed it more than once while snooping for something bad in the wiring.

But I am certainly no mechanic.

Will double check mine as well in case I missed anything.

So, new (used but original) regulator arrived.

Tested old one again and again still only showing 12.2v at battery regardless of revs.

Put the new/old regulator on and varies, depending on revs and lights, 13.5-13.9v

So safe to say the Chinese regulator gave up after 1 years use

Couldn't find any chaffing of wires (apart from a tiny tiny bit but not near cutting through) so now fingers crossed.

Awesome! Those new numbers sound much better. I think you've solved your problem -at least I hope you have. Coming from a family of electrical engineers (I'm certainly not one) electrical issues anywhere and in anything have me baffled.

No more kicking and cussing???

I'm just glad I didn't have to go down the stator route.....

But at £9 to fix I'm very happy and the bonus is the bike has had a virtual electrical mot with me having checked for a parasitic drain and chaffed wires

I am surprised at how hard it is to find new genuine regulator though..... Still no idea where to get one......

At the end of the day, and while it's my wife's bike (I ride a Triumph Sprint ST1030), I still have love for the little Vespa

Did you try the dealer??? Part is still sold by Vespa.

When I bought Chinese one last year I tried local dealer but they were hopeless, didn't even know what an ET4 was!

But if I need another I would phone round others further afield.