It's been a long time since I even looked at the theory of recips, but I seem to remember that the first generation rotary aviation engines were single valve (exhaust only) engines. They worked somewhat like a two stroke for induction. That is, the fuel/air mixture passed through the crankcase on its way to the cylinders. It got into the cylinder via a port at the base of the cylinder when the piston was down. This allowed for a light simple valve operation, but didn't allow for a throttle. These engines ran at either full speed or no speed, which is why you hear them cutting out on approach (at Rhinebeck or the movies), they couldn't throttle back so they just cut spark and coasted for a few seconds.