Abstract: A carburetor of an internal-combustion engine in an automotive vehicle has at least one main duct and an ancillary duct supplying an air/fuel mixture to a manifold, the fluid flow through the ducts being controlled by an accelerator via ganged butterfly valves of which the one in the main duct closes completely whereas the one in the ancillary duct closes only partially in an idling position. Separate nozzles deliver fuel to the main duct at a higher hydrostatic head and to the ancillary duct at a lower hydrostatic head, thereby preventing the aspiration of an excessive amount of fuel by the piston cylinders upon deceleration of the vehicle or during idling. The fuel is admitted to the ducts, between a Venturi throat and the butterfly valves, by nozzles fed from a common float-controlled pressure regulator, or from two such pressure regulators, to which the fuel is delivered by gravity from a buffer reservoir also provided with a float valve and connected to the high-pressure side of a fuel pump.