Modern Vespa

Yes thanks... But there is not much info on the NCV 20.. I'm wondering if it could be the screw on the float bowl?.. Or if many the screw is covered by and aluminum cover..

Corsa Meccanica has an parts diagram here;

http://corsameccanica.com/carburetors-components



But I'm not sure which screw corresponds to the mixture adjustment (perhaps #17 Adjuster screw?).

Thanks buddy.. Yes I found it, thanks again

You appear to have bought a Dellorto jet, What you have is a standard Keihin CVK carb, and takes either the same 4mm or 6mm jet as the keihin carb for chinese clones and Yamaha Vino models. You should be able to get them anywhere that sells or works on scooters. If it takes the 4mm, we have a jet kit for about $16 with a whole range of 10 different size jets, but I'd have to open up one of those carbs to see which jet it takes. If it takes a 6mm jet, it is difficult to find them that small, because most of the carbs that take the 6mm jet are for the 125-150 chinese carbs. From the photo, it looks like a 4mm jet.
Don't expect much, if any change in overall performance of the bike from changing out the jet, and if you overjet, the bike will slow down.

So I found the mix screw, managed to get it off with a flat head screw driver, since it's a D shaped head. I cut a flat slot into it with a hand saw, and I adjusted the mixture with a flat screw driver. And it's seemed to have fixed the hesitation the bike was having off idle acceleration. I've been having the problem since day one with the Vespa, seems to be have been Mia adjusted since fabrication.

For those in North America with a (stupid!) D-shaped idle mixture screw instead of a rest-of-the-world standard slotted head - get a bit of (brass, whatever) tubing that just fits over the D, and then put a flat in it.