Multiple cylinder internal combustion engine having mixture cut off means

Internal combustion engine comprising a plurality of cylinders, first intake passage means leading to at least one of said cylinders, second intake passage means leading to the remainder of the cylinders, said first intake passage means including for each cylinder associated therewith a first primary passage and a first secondary passage which are separated from each other, said second intake passage means including for each cylinder associated therewith a second primary passage and a second secondary passage which are separated from each other, primary throttle valves respectively provided in said first and second primary passages and having minimum opening positions, secondary throttle valves respectively provided in said first and second secondary passages so that the secondary throttle valves are opened only for heavy load operation of the engine, means for supplying combustible mixture to said passages, shut-off valve means provided in said first primary passage downstream of said mixture supply means and movable to a closed position for blocking the supply of the mixture to the cylinder associated with said first intake passage means, means for detecting that the primary throttle valve is in the minimum opening position and moving the shut-off valve means to said closed position when the primary throttle valve is in the minimum opening position, means for providing a supply of air to said first secondary passage, control means sensible to engine speed and throttle valve position and controlling said air supply means so that a substantial amount of air is supplied to said first secondary passage when the throttle valve means is in the minimum opening position and the engine speed is below a predetermined value but the air supply is essentially interrupted when the engine speed is beyond the predetermined value.