I have been told by the shop owner who sells Zuma's (under another name)... that all you have to do is unplug a certain wire and the rev limiter will be disconnected.
This shop owner is an ace mechanic and racing engine builder... not some white collar dork salesman.
There might also be a plastic washer on the variator that prevents the pulley from closing all the way... (little more speed)
... he says there is a small kit that goes with it (maybe carburetor jets ?)... that lets it go a little faster yet.. (along with the rev-limiter unplug)
For right now ?... Leave it alone... break it in and learn to ride and get used to it.
Put 1000 miles on it then worry about making it faster.
43mph is pretty good isn't it ??
Zumas were designed and built by Yamaha in Japan ... but they farmed the production out to Korea and they are made there now and sold under the Yamaha name and a few other names (same machine).
They are good machines.