Membrane fuel pump with pulse dampener

A membrane fuel pump for an internal combustion engine for a work apparatus and especially for a handheld, portable tool such as a motor-driven chain saw and the like, the engine having a piston and a cylinder conjointly defining a combustion chamber and having a crankcase wherein pressure is developed in response to the movement of the piston, the engine being equipped with a fuel tank and a carburetor having a pressure controller, the membrane fuel pump comprising:

• a housing defining an enclosed space;
• a membrane partitioning said enclosed space into a drive chamber communicating with said crankcase so as to be charged with the pressure therein and a pump chamber;
• said pump chamber having a suction end connected to the fuel tank and a pressure end connected to the pressure controller of the carburetor;
• first check valve means interposed between said suction end and the fuel tank;
• second check valve means interposed between said pressure end and the pressure controller of the carburetor;
• bypass means interconnecting said pressure end and said suction end for bypassing said pump chamber and passing fuel from said pressure end back to said suction end;
• and,
• throttle means arranged in said bypass means for throttling the flow of fuel passing through said bypass means.