Four-stroke engine

The present invention relates to a four-stroke engine. DE 42 27 433 C2 discloses a four-stroke engine for portable implements and has a diaphragm carburetor, whereby for the drive of a fuel pump of the carburetor, the pressure pulsations in the intake pipe between the carburetor and the cylinder are utilized. For this purpose, a pressure chamber of the intake channel communicates via a pulse line with the drive chamber of the pump. During operation of such four-stroke engines, it has been shown that the pressure fluctuations in the intake pipe are not always sufficient for driving the fuel pump. In particular during acceleration, during rapid opening of the butterfly valve of the diaphragm-type carburetor, a break in pressure occurs that limits the fuel supply. A four-stroke engine is provided and has a cylinder and a piston that delimits a combustion chamber and by means of a connecting rod drives a crankshaft disposed in a crankcase. To drive a fuel pump, the fluctuating inner pressure in the crankcase, in the valve housing or in a connecting passage that connects the two housings is utilized. For this purpose, a drive chamber of the fuel pump is connected via a pulse line with a crankcase, a valve housing or the connecting passage.