One of these was my first motorcycle. It had been hot-rodded with a high compression head, a "competition" rotary valve, and a very loud Bassani expansion chamber exhaust. It would do right at 55MPH at the top of fourth gear.
That was followed rapidly by this light-switch power, 90cc brick. It had a 100-tooth rear sprocket, so it was fairly quick, but it would bog if you let the revs down (no reed valves). The no-name aftermarket expansion chamber exhaust was also exceptionally loud with the silencer removed. Ours (I have 2 brothers) was an HT-1B motocross version and was never fitted with lights or steel fenders. We used Preston Petty replacement fenders whenever it got tossed around too much.
Eric