Abstract: An air filter for filtering combustion air for an internal combustion engine includes a housing holding a filter element and an inlet snorkel tube connected to the housing. A "trap door" valve mechanism is located in the snorkel tube and includes a valve seat mounted on a support which circumscribes the inner wall of the snorkel tube and a valve element pivotally mounted on the support which is yieldably urged into sealing engagement with the valve seat when the engine is turned off. The valve mechanism presents a surface substantially transverse to the direction of air flow through the snorkel tube, so that combustion air communicated through the snorkel tube when the engine is running acts against the transverse surface urging the valve element to an opened position. The valve element is "cracked open" by a solenoid when the engine is to be started in order to permit initial air flow through the air cleaner to facilitate starting.