Abstract: A carburator for use in combination with an intake manifold for a multi-cylinder internal combustion engine wherein the manifold has two sets of related tunnels to conduct fuel and air to related sets of cylinders, said carburator having two venturi throats, each related to one set of tunnels, throttle valves in the throats, an air conducting throat related to one set of tunnels, a shut-off valve in the air conducting throat related to one set of tunnels, a shut-off valve in the air conducting throat and means operable to selectively open and close the shut-off valve and to maintain the throttle valve related to said one set of tunnels closed when the shut-off valve is open, whereby the engine can be selectively operated on all cylinders or on only those cylinders with which the shut-off valve is not related.