how to get a higher top speed

Hi, I have a Vespa 50 (1964) and I’m trying to tune it up with all the money I have. I have already got a racing barrel, piston and crank. I am just wondering if anyone knows the best way to get to higher top speed, yet keeping the engine as a 50. Many thanks for replies, jordan



mount these two parts -  and you start to  "fly"