Back 30-some years ago, I had a Yamaha U5E. 50cc Electric start w/3-speed gearbox. It had a centrifugal clutch. All 3 gears was down. It had a double-ended shifter so it was easy on shoes. Just had to step down on the back end of the shifter to down-shift. It would top out about 35MPH before I bored it out to the gills. Got a little over 40 after that. Here is a pic of one. Not mine but one I found on the web.