I never had any experience with Yamaha 50's, but spent many an enjoyable hour on a "Kermit Green" Suzuki AC50 Maverick (or perhaps it was an AS50?) My first "real" motorcycle, modified with knobby tires and a smaller front sprocket for some modest off-road capabilities. Most interesting thing about it was you could get the engine to run backwards if you popped the clutch while rolling backwards down a hill. It didn't run great, but it certainly was firing in reverse. Don't recall what antics I was up to when I discovered that... Must have been some interesting rotary valve timing on the thing.

This one was not mine, but it's exactly like it: