Those XR75's in YZ80 frames were a big thing back then. Twice the weight with half the horsepower.
Gangs of fun! It's a legacy that last 'till today......
They even had a special 4st race so they could win.
Some XR75 had thousands spent on them in the late '70s so they could be slower than an RM or YZ80 but did make a different noise.
Ahh the memories an XR75 bored out, HIComp piston, oil cooler, meg dollar ignition, big valves, ported and polished, big cam, big carbie on methanol, unbaffled pipe, in YZ80 chassis out gunned by a standard off the show room floor RM80/YZ80.
I had a Honda SL100/125 back in '72 or so and thought it was the ducks guts until I saw and rode a CR125. I still remember the look on the faces of kids with XR75s when this kid showed up at our club with a YZ80B (silver tank from memory) and all they saw was the bit of blue smoke after the first corner.