Modern Vespa

I have been riding my new (old) scooter for several months now. sometimes when i come to a stop and push in clutch & brake my engine does not slow down. My hand is not on the gas. The engine is revving super fast and there is nothing i can do to slow it to its regular idling speed. It usually will fix itself after light turns green and i take off once more. But this can't be good for it.

what happens when the engine is running and you pull out the choke?

If i leave the throttle pulled out too long the engine starts to sputter and die.

sounds like an air- leak to me. on a smallframe, air leaks often stem from a loose connection at your carb. make sure that your really snug that thing on, and make sure the felt washer is in there. Also check your carb slide and throttle cable - a little stickiness is common but when you let go of the throttle it should return to normal.

8)

+1

or check crank shaft oilseal

If it has leaking promblem, it can cause idle problem too.