Re: Higher flow petcock?
I had a similar problem, and i ended up taking the petcock to the hardware store and i found a miniature ball valve with the same threads, but when i went to a different hardware store for another they didn't have it. So just find out the diameter and thread count by using the tool for that purpose at the hardware store, and order it online if you cannot find it. Or there is always using a spring clamp on the fuel line. That works well if you fold over a bit of the line and clamp it. Good luck!
My motorized bicycle is cooler than your Vespa, even though you can go faster.