quickly stalling the engine, or damaging the cylinders). Early models featured a pioneering form of variable valve timing in an attempt to give greater control, but this caused the valves to burn and therefore it was abandoned. The only way of running a Monosoupape engine smoothly at reduced revs was with a switch that changed the normal firing sequence so that each cylinder fired only once per two or three engine revolutions, but the engine remained more or less in balance. As with excessive use of the "blip" switch: running the engine on such a setting for too long resulted in large quantities of unburned fuel and oil in the exhaust, and gathering in the lower cowling, where it was a notorious fire hazard. "Normal" rotaries Most rotaries had normal inlet valves, so that the fuel (and lubricating oil) was taken into the cylinders already mixed with air - as in a normal four-stroke engine. Although a conventional carburetor, with the ability to keep the fuel/air ratio constant over a range of throttle openings, was precluded by the spinning crankcase; it was possible to adjust the air supply through a separate flap valve or "bloctube". The pilot needed to set the throttle to the desired setting (usually full open) and then adjust the fuel/air mixture to suit using a separate "fine adjustment" lever that controlled the air supply valve (in the manner of a manual choke control). Due to the rotary engine's large rotational inertia, it was possible to adjust the appropriate fuel/air mixture by trial and error without stalling it, although this varied between different types of engine, and in any case it required a good deal of practice to acquire the necessary knack. After starting the engine with a known setting that allowed it to idle, the air valve was opened until maximum engine speed was obtained. Throttling a running engine back to reduce revs was possible by closing off the fuel valve to the required position while re-adjusting the fuel/air mixture to suit. This process was also tricky, so that reducing power, especially when landing, was often accomplished instead by intermittently cutting the ignition using the blip switch. Cutting cylinders using ignition switches had the drawback of letting fuel continue to pass through the engine, oiling up the spark plugs and making smooth restarting problematic. Also, the raw oil-fuel mix could collect in the cowling. As this