The intake and exhaust control systems are operable in varying modes, according to the engine speed, by a single actuator. The intake control system includes an intake valve that allows a variable amount of air into an air cleaner depending on vehicle speed. The exhaust control system includes an exhaust control valve, and a primary and a secondary exhaust purifying system located downstream of the exhaust control valve. The flow into the exhaust purifying systems may also be controlled according to engine speed.