The rotary valve Kaw 100 was one of my first trail bikes. Great motor.
The development of the reed valves allowed more efficient "packaging" of the motor.
Efficient packaging is one thing, but the rotary valve was by far the superior of the induction system on a two stroke. The rotary valves did make a "WIDE" motor. But in the case for the Bridgestone twins, it made an ideal place for the dynamo right behind the cylinders. Most two strokes back then were piston port and you could clip the skirt a bit to change timing. We also used to cut down the top of the piston to match the exhaust port to gain a bit more exhaust timing when we ran tuned pipes.
Oh those were the days!!!

On my 175 Bridgestone that I stripped down and ran in the woods, I had the center crank seal go out on me and it was passing crankcase fuel/pressure back and forth within the crankcase, didn't run good that way. So I took the crank over to a friend that owned an injection mold shop and he had a hydraulic press. I pressed the crank apart and rotated one half 180 degrees making both cylinders go up and down at the same time, like a BSA or Triumph. Bridgestone didn't sell center crank seals, only new cranks and I was a kid and cheap. I also corked the crank holes to help build a bit more crankcase pressure. I now had a twindle. It wasn't quite as fast, but it did have a bit more low end for a two stroke. It also had a nice sound to the expansion chambers. I did some really stupid things way back when. But by todays standards, I guess it was pretty lame actually.
Sorry again for digressing guys.....
