3 restrictions on this bike.
Variator boss, carb jet, and muffler. Easiest thing to do is buy a new variator because they usually come with a new drive boss. You will need an electric impact wrench or figure out a way to hold the variator while you unscrew the variator nut. Upgrade the carb jet (search this forum for size). The muffler can be left alone but to de-ristrict it you can cut off the extra emissions tubes and weld the hole shut.