Modern Vespa

Hi all,

I've scrolled these forums up and down for some months now, tried all the fixes from people with similar issues, yet my issue still seems to persist.

As the title says my Vespa has intermittent starting issues with no apparent reason (not something I could figure out) but mostly when starting from cold sitting in the garage at room temperature, regardless if it was ridden for long or short before.

2012 Vespa GTS 125ie, 17800 kms

Issue:
Immobilizer LED blinks one long on ignition
Starter cranks fine
After engine cranks it sounds like the engine starts for like 2 revolutions then it cuts out
Cycling the key on/off then trying again does the same thing, until it cranks long enough that I can give it a bit of throttle that keeps it alive. After this all is perfectly fine.
Sometimes it starts straight away with no issues.

Troubleshooting done(I'm not a mechanic but i'm pretty handy with tools):
- Battery checked, all good (tightened connections as well)
- Fuel pump tested and primes well on ignition
- Injector cleaned
- Valves adjusted
- cleaned idle bypass
- Spark plug changed (spark plug lead looks in good condition)

What did I miss? What else to check?

Cleaned the idle bypass? (Not sure if the 125 has one?)

Yup, did that too. (added to the list)

Earth leads can cause some strange issues and are easy to check / replace.

Is the coolant level stable? Is there any coolant in the oil?

Have you changed the air filter, and can you see if the exhaust is clear - sometimes mice have a habit of making nests in the exhaust if the Vespa has been left for awhile.

At some point, you might have to consider going back through your list again - are the valves definitely adjusted to the correct value?

Is it worth pulling the spark plug and seeing the new colour?

EDIT: The brake light has to be illuminated for the Vespa to start. When you are trying to start the Vespa, is the brake light on? No flickering?

Dodgy kill switch?

he said it cranks so not kill switch problem

Coolant level is stable. It was a bit under minimum so i topped it up. No coolant in the oil.

I feel it's a fueling issue, but with the pump and injector working fine I'm not sure what else to look into.

No idea what would cause such a random intermittent issue, once in a week, or every 2 weeks.

Dodgy kill switch might let you crank and then the vibrations screw with the dodgy contact. I had a dodgy kill switch that would cause a stall just after starting if you went over a bump.

Fair point

I tried jiggling the kill switch while the engine is running to see if I can notice any sign of it being dodgy, but it seems to be solid in the ON position (I would expect if it would be dodgy, it would try to cut out at least a bit while moving it around)

I've seen it topic154345 and topic68491 that it can cause issues similar to what I'm experiencing so might as well order a new one and see if it fixes my problem.

Cheaper to cut the wires and join them together. I do it on all my bikes.

Hi all,

While waiting for the kill switch to arrive I managed to get the starting issue on camera.

https://youtube.com/shorts/2APb4IS5jUM?si=PRqAKW3CuVF6y1kj

Any idea what it could be?

As JakeM asked, have you checked the air filter?

I cleaned the filter last year(had a bit of oil on one of the corners but not dirty otherwise). The starting issue was the same before and after.

I've ordered a new malossi filter together with the kill switch. Once they arrive I'll pop them in see if it would make any difference.

Maybe check the spark plug lead connection at the other end.

Checked the cable as well. Took it out cleaned it. Checked for cracks.

All looks good, contact to the coil is solid.

While still waiting for the kill switch and air filter, another issue seemed to have come up.(intermittent starting issue still there )

After riding a bit and the engine warms up, while pulling up to a light the idle stays very high (having to hold the break not to move). It almost feels like the throttle getting stuck slightly open. Turning off by the key and restarting brings the idle back to normal (if i shut it off from the kill switch and restart it afterwards the high idle stays)

Is there some sensor (O2, temperature, etc.) that might have gone bad, causing the starting issues, and now the high idle?

LE: Seems the exhaust gasket is failing, it's leaking a lot, if I plug the end, the engine speed barely changes. -could this cause any of the issues?

The failling exhaust gasket could cause issues, when your GTS has a lambda sensor, but I don't think the 2012 models already have such a sensor. And even with a sensor, the system would think there is too much oxigen in the exhaust, and therefore enrich the mixture.
Another possible cause, as you mentionned, is a defective temperature sensor. Do you have the same problems sometimes with the engine warm or hot? And if not, does your GTS has a temp gauge? If your sensor doesn't tell the ECU the engine is cold, then the brain will not add extra fuel, and the mixture will be too lean (works the same way the choke on a carb engine does).
The stepper motor in the throttle body can also be failling, but that would be subject of diagnose with special software and tools.
And has somebody in the recent past tried to change the idle rpm by fiddling with the idle screw on the throttle body? Because if they did, you will need the same diagnostic tool as mentioned above.

Hi guys,

Got a bit of an update.

1. Exhaust gasket replaced
2. Air filter replaced
3. Kill switch replaced (old one looked a bit corroded)

I really hope the issue will finally be fixed.

Well, the saga continues, this morning the vespa decided not to start again.

I tried about 4-5 times. Just as before, it fires up initially, but then straight away dies after 2-3 revs.

If I manage to time it well, after startup to give it a bit of gas so it stays alive, and rev it to about 10-15% for 30 second, then it stays on and does not stop.

It makes me believe that a sensor (maybe O2?) or the ECU is having issues.

Any idea how I could test them?

Hey guys,

I've managed to capture a bit longer video with the starting issue.

https://youtube.com/shorts/h_oVIwjLFzQ?feature=share

Any suggestions would be greatly appreciated.