Modern Vespa

Good afternoon,
Not a frequent visitor to the site in the last few years but 10+ years ago when I first purchased a 2002 150 I found the site most valuable! What a resource for a scooter owner to "mature" in the scooter world - Thank You, Thank You and Thank You!

So after having a couple of 150s, I moved up to a GTV 250 in 2009 and then a GTV 300 in 2014. This last sat quite a bit as I was working out of town .

Not sure what triggered it, but the engine now stalls when at idle. Have searched and read every post I could find here to explore the cause. Some of the items I have performed.
1) drained the gas tank.
2) ran a can of SeaFoam thru the engine.
3) checked voltage of battery - 12.5v when turned off, 13+v with engine running.
4) injector - removed and cleaned as taught by Robot - WOW what another resource - Thank you Robot.
5) disconnected battery for a day, connected, started and hoped it would idle. Read that the this may be a way to reset the ECU.
6) cleaned air filter.
7) have ran more than 3 tanks of fuel thru it since and runs fine at all speeds above idle.

AND the engine still stalls when throttle released.

Nearest dealer is in Savannah GA, bit more than 1 hour away. Called and requested to make an appointment for a diagnostic, as I could ride the scooter there. They would not make an appointment; their method of providing service is to have the scooter dropped off and in a few weeks they will get will get back to me. Not sure how long they have been a Vespa dealer, but the prior dealer was very customer/user friendly. Believe they may specialize in larger two wheelers. No other dealers close by

Any suggestions???

And again thanks to all those who contribute to this forum - GREAT resource for us

Classic symptom of a blocked idle bypass passage. Clean it.

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

Hey Jim - Thanks for the response!

I took the carb body out and flushed the "by-pass" out with carb cleaner. Installed and improved, but still will not stay running. Removed and cleaned again from intake end to engine side. Then flushed from engine side to intake end. Still not back to par and will run for a bit longer, maybe 10 seconds.

Do I need to dis-assemble the carb body and clean the by-pass valving?
If so, any instructions on that procedure?

Thanks!

First - it isn't a carb, it's a throttle body. Just as carb cleaning can take several goes to really clean jets etc of all gum, the same applies to the throttle body. You can also check the inlet manifold (the bit between the throttle body and the engine head) for any cracks, as that also won't help idling.