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rotary valve is an opening on the crank web, the size and position of the web dictates the size and duration of inlet port opening (the exhaust port is controlled by the piston) old Vespa engines are like this.
piston porting is just that . . . .as the piston goes up and down it opens and closes the port at the bottom of the barrel . . .Lambretta engines do this, you can modify the piston skirt and port size to alter inlet timing, size and duration.
reed valves, I think, work on a non return basis, and are further up the barrel controlled by the piston top ( I could be wrong here)
from my knowledge of scooters performance is reeds best, piston 2nd, rotary Vespa! (very reliable though)
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