Thermostatic Air Cleaner: Operation

The intake duct allows cold outside air or heated manifold shroud air to enter the carburetor, depending on the setting of the duct door. The door position is controlled by a vacuum motor which responds to various vacuum signals from a bimetal sensor in the air cleaner housing. During cold engine operation, the snorkel door is in the up, or heat on position. Only heated air from around the exhaust manifold is allowed to enter the carburetor. As the temperature inside the air cleaner warms up, the bimetal sensor bleeds off some vacuum and the snorkel door moves to allow some cooler outside air to enter the carburetor. When full normal operating temperatures are reached, the door will be down, allowing only outside air into the carburetor.