and distributing valve 10 at the same time the internal combustion engine draws air through the suction tube 1 and as a result the air sensor 2 undergoes a certain excursion from its rest position in response to the deflection of the air sensor 2 the control plunger 14 is displaced via the lever 11 and thus the fuel flow passage section at the control slots 30 is increased the direct connection between the air sensor 2 and the control plunger 14 ensures a constant ratio between the quantity of air and the metered quantity of fuel provided the characteristics of these two components are sufficiently linear which is desideratum by itself in such a case the fuel air ratio would be constant for the entire operational range of the engine however it is necessary for the fuel air mixture to be richer or leaner depending on the operational conditions and this is achieved by varying the restoring force acting on the air sensor 2 for this purpose there is provided in the control pressure conduit 38 and electromagnetic valve 42 and a pressure regulating valve 44 which by influencing the pressure of the pressurized liquid during the warm up phase of the internal combustion engine influences the mixture enrichment in dependence on.