Abstract: A carburetor for internal combustion engines with an acceleration pump whose pump chamber is connected to the float chamber by a suction duct having a suction valve. The pump chamber also is connected to the intake line section upstream of the throttle by a delivery duct having a pressure valve and a calibrated injection opening. The acceleration pump has a displacement member which is actuated via a linkage by a lever depending on the throttle position. The pump chamber has a flow duct, leading to the float chamber and having a cross section adjustable by means of a screw, and a second adjustable flow duct whose inlet has a valve actuated by the throttle position. The valve may have a spring which presses a closure member, held in a diaphragm, against the inlet overcoming the force of the fuel pressure. This spring also presses a plunger against a second lever arm which actuates the acceleration pump.