This was almost literally true of the "Monosoupape" (single valve) type, which took most of the air into the cylinder through the exhaust valve, which remained open for a portion of the downstroke of the piston. Thus the richness of the mixture in the cylinder could not be controlled via the crankcase intake. The "throttle" (fuel valve) of a monosoupape provided only a very limited degree of speed regulation, as opening it made the mixture too rich, while closing it made it too lean (in either case quickly stalling the engine, or damaging the cylinders).