Do some More reading around
E.g look for a kit with a reed valve intake
This will help you rev higher, and they generally make more hp then piston port kits.
If you’re feeling handy and want to do your own modifying you could look around and see how other people have ported kits you’re looking at. This can be done quite cheaply and easily and will only add to your power!
I run a 70cc Puch Maxi does 58mph and out accelerates my friends Kawasaki ar80