An internal combustion engine has an intake channel which opens via a first valve into a crankcase of the engine. The first valve opens at a first frequency (f1). The engine has a second valve, which controls the quantity of fuel supplied into the intake channel. The quantity of fuel is controlled by controlling the time interval during which the second valve is open during each engine cycle (x). A control device is provided to control the quantity of fuel supplied. In a first operating state, the second valve is opened at a second frequency (f2, f3, f4) which is coordinated with the first frequency (f1). In a second operating state, the second valve is opened independently of the first frequency (f1).