I always use Nova carbs on my Piccos. It just needs a 5 minute session on a lathe, and it will fit. Nova carbs are much better in my opinion.
Just put it on and you will hear the difference, even on the starter box!
The engine will respond better with 9 mm restrictor, opposite to Novas which usually improve just on hi revs. Piccos gain torque always from low to hi rev, when using larger venturis. Bench tested.
ciao