Modern Vespa

I just bought a 2010 Vespa LX50 that has about 4000 km, 2500 miles on it. It had bad starting, idling issues and seemed a bit lazy. We brought it to a repair shop that changed gas and vacuum hoses, spark plug, intake manifold and in the end the whole carburetor. Now it runs otherwise smoothly, but the repair shop said that the new carburetor is running too rich with enricher on, and the scooter does not idle at all while enricher is on after starting, it shuts down without throttle. The problem is just with idling, from the get go it runs well. After a few minutes of riding it runs perfect and idles normally. Also I read a bit somewhere that a scooter is supposed to start without cranking the throttle, my scooter always needs just a bit of throttle to start, but does so without problem. They said there is really nothing that can be done to the scooter running too rich after starting, and maybe it will idle better when the temperatures get a bit colder. I refuse to believe that nothing can be done to it running too rich with the enriching/autochoke on, is there something that could be done? My experience with motors and scooters is close to none, but I'm a quick learner and work well with tools.

Because of environmental laws, air cooled scooters with carburetors are set up to run as lean as possible. You can change the idle jet to a 38. That usually smooths out the idle. Also, make sure the idle jet is clean. Even on new ones, it can come in with debris blocking it. And ask the shop if they set the air fuel screw or just put it a certain number of turns out. A lot of newer technicians sadly don't really know how to adjust the air/fuel screw on a carburetor. The scooter has to be very warm, and that takes time, which isn't something a tech being paid by the job often wants to use to warm up an engine.

The new carburetor already has a 38 idle jet and the mixture screw is set, they said from the repair shop. I tinkered with the idle speed screw, and seemed to mess something up. After adjusting it for a few times first tighter, then looser, now the idling turned very uneven. I can't seem to find the right adjustment. After adjusting it when the engine is warm to what seems like a good idle, then after riding for a bit and idling again the engine idles too fast making the scooter accelerate when stopping for red lights. Then the next stop the engine might faulter as the idle speed seems too low.

Replacement was factory carb?

I'm not sure what you mean by factory carb, English is not my first language. It's a cheap 18 mm aftermarket carb, not sure of the brand

Factory carb, Keihin NCV20, $600 from Vespa, about $250 aftermarket.

Cheap Chinese carb might be your problem.

The running too rich with e-choke on might then be a quality that can't be adjusted away, or?

But now I'm running into the new problem of uneven idle after messing with the idle screw. After e choke is off, the idling can alter from faultering while stopped to red a light and running too high in the next. What can cause this?

Is this your carb?

https://www.easyparts.nl/Carburateur-Keihin-NCV-20-AR3-PIAGGIO-Fly-50-4T-4V-E2-2012-2013-p33527534

The price of the carburetor was 60 euro (70 USD) in the repair bill, so not that one.

Did the shop give you the old carb? If so, maybe try cleaning and reinstalling it.

Or maybe try swapping the enricher from the old carb onto the new one if it will fit.

They did not give me the old carb, I asked if it would be wise to take it and they said that it's a paperweight so no use of taking it. They tried cleaning and checking everything in the old carb before changing it to a new one.