Modern Vespa

Hi,

Got my second Vespa, this time 2015 Primavera 125 Touring with 3 valve injection engine.
5400miles on the clock.

The bike was not used for over a year now. So after cleaning and checking everything is working well, I found a bit annoying problem, when gently touching/turning acceleration handle, the engine is stalling, it's struggling to rev up.

I did pour Liquid Moly to new full tank of super petrol (97 octane) still 3/4 full, cleaned the injector with carburettor cleaner and this DIY kit.

This is the video of my problem:
https://youtu.be/flbUD8j2izk

Could it be the throttle issue?

My initial thought is that it could be related to the drivetrain / clutch.

I've noticed mine is a bit glazed from crawling in slow traffic - it seems to much prefer full throttle launches. I'll have the clutch sanded down soon when the drive belt is replaced.

Other thing to check would be the valve clearances. These are meant to be done at 620 miles, and then I think at every 6000 miles - but are often ignored.

I did valve clearance last week, I did clean all connectors around the engine as well.

It feels like the throttle is opening and there is no fuel enough coming from idle to higher RPM. My thoughts are the throttle sensor, but how to check it?

When I rev the engine before take off. It's runs great.

With my glazed clutch, as I pull away at low speed, it feels like it sticks - then it makes a screech sound, and then everything is ok.

If this was any worse, then this sticking might be enough to stall the engine?

I'm not sure if we have an OBD port on these Vespas to read error codes / throttle position sensor position? Mine has the Vespa MIA app which lets me view rpm etc on my phone - but this might not exist on a 2015 model, you might have to manually plug in a little computer to see this data?

I would try doing the same gentle throttle opening at the motor just for fun. I'm not sure what it would tell you if it stalls or not tho.

On listening to the video again, there's an almost metallic tapping sound that doesn't seem normal to me. Maybe the valves are at the wrong values?

I set them to 0.10 and 0.15, as per manual

At local service, they told me to use 2 - 3 fuel tank to clear the system, I'm still struggling to finish the first one

This is under the assumption the carburettor has already been cleaned:

Check the accelerator pump is working. This is the part of the carburettor that squirts an extra bit of petrol into the intake manifold when the throttle is opened. If you remove the carb (but keep the throttle cable and fuel connected) and twist the throttle you should see a stream of petrol being squirted out.

This one is with the injection system, there is a throttle body with sensor.

I cleaned the injector only with a spray kit, now have 1/3 of fuel with liquid Moly cleaner.

OK, my apologies - I just saw '07 LX125 in your profile... Have you cleaned the idle bypass passage?

Did not do it, I did not know there is one.
Only soaked cloth with carburettor cleaner and wiped the throttle flap and sensor connector plug.

See: https://cheekythoma3.wixsite.com/itsme/idle

I did found this on my Service Manual for Primavera with 3V injection.

To obtain the optimum fuel mixture, especially at small openings of the throttle valve, it is essential to
match the throttle body with the control unit following the procedure known as TPS resetting.

I think I may have this issue, with wrong settings of the throttle body.

Indeed - and it's only to be done with a new throttle body!

So I will ignore it, now will use this 1/4 of fuel I'm left with, than fill up again full and use liquid Moly again.

Tomorrow will take out the throttle body and again clean it properly with carb cleaner.

Today I took the engine off the frame to check everything once more time.
Took the throttle body out, cleaned it with carburettor cleaner, the little idle air bypass is/was clear. There was some residue around the butterfly throttle valve. I think JakeM you have been correct, I did valve clearance again and now it looks like my problem disappeared 😄👍
The clearance was way bigger than recommended 0.08mm on both intake and exhaust side.

So this means I did the clearance before wrong.

Now I will ride it a bit and do more checking ✅

Good man for getting in there and sorting it out.

Well, after setting the valves, I still had the same problem with bike choking on little throttle acceleration.

I try to book service in my local Piaggio shop, but it they were always busy and the bike needed to stay there for 3 to 4 days.

So I decided to risk and I got myself a diagnostic tool for all sorts of bikes, included my Primavera first generation 125cc with EFI PRG04 ECU.

It cost me £380 with shipment from PL.





This is the software they providing with the hardware



I can basically do this things:
EFI TECHNOLOGY PGN04 / PGR02 / PGR04 / PGS02 / PGS06
✓ Read Identification and immobilizer status
✓ Read / Erase diagnostic trouble codes (DTC)
✓ Reset throttle position sensor programming (TPS)
✓ Reset self-adptive parameters
✓ Read / Write VIN (if in use)
✓ Read / Set keys
✓ Read / Write MAPS (for chip tuning or de-restriction)
✓ Reset to VIRGIN
✓ Set IMMO-ON / IMMO-OF


So yesterday I did a reset of my TPS sensor position, read some stored DTC error codes and simple info from my Primavera 😁

Now after TPS sensor position was reset, all works like new 👏

Connection is really fast, I don't think there is a lot of data to exchange, probably just bits of code via K-Line.

I'm really impressed with how simple to use is this hardware. I can only recommend it to all users.
If you have any info, please feel free to ask. I will try to do a video of how to use this soon 😁👍