How are rotary engines controlled?
Some of the early radial engines that operated by rotating the entire engine along with the prop, specifically, the very popular Le Rhone didn't have proper throttles. The pilot controlled engine speed by switching the ignition on and off. 

This wasn't so much a limitation of that particular design, as a limitation of engine tech in general at that time. Wilhelm Maybach first devised the jet spray carburetor (patterned after a scent spray) in 1893, but the throttle body didn't appear for another ten years. Those early engines had only two speeds: wide open, or off. 

Thus, the reason that many of the early WW1 fighters are constantly revving their engines on the ground... the pilot was switching the ignition on and off. Must have made for interesting ground handling.