When I was a kid, the father of one of my friends had one of those Yamahas. A year or so later he traded it for a BSA Thunderbolt; one day when he was at work my friend and I took the BSA for a joyride, he was 13 and I was 12.
I remember we were going down a gravel road at about 80mph...not a smart thing to do, but we survived and his dad never found out.