Abstract: An intake system for an internal combustion engine includes first and second intake valve bores provided to face a combustion chamber and to be independently opened and closed by first and second intake valves, and first and second intake ports which are connected to the corresponding intake valve bores with a partition wall interposed therebetween and which communicate with a common intake passage. In a particular operation range of the engine, an imbalance is produced in the concentration of the air-fuel mixture flowing through the first and second intake valve bores into the combustion chamber on the basis of a difference between the amounts of fresh air flowing into the first and second intake ports. The intake system further includes a communication hole provided in the partition wall for putting the first and second intake ports into communication with each other. This provides for improvements in the lean combustibility and in the nature of the exhaust gas.

Abstract: An air intake device for a motor vehicle with a riding saddle, having an engine, an air cleaner disposed behind the engine, a tube defining at least a portion of an air intake passage from the air cleaner to the engine, and an exhaust passage extending rearwardly from the engine alongside of the air cleaner. The tube has an end connected to a side of the air cleaner remote from an opposite side thereof along which the exhaust passage extends.