if youre going to get a carb, dont bother buying the 22/25. get the 15.15 with custom intake from 1977mopeds/motion left, and just jet down. that way, if you want to go port or get a abetter exhaust, you dont need to upgrade your carb. the biggest, immediate improvement would be getting the larger header pipe. if you need it, i have the expansion chamber that fits it, just not the pipe.
also, the pipe itself is pretty easy to make if you have access to someone to a metal shop.