Intake Manifold (Carbureted Engines)
Intake manifold has a preheat chamber and secondary throttle plates for each carburetor. When engine is idling and during normal driving, secondary throttle plates are closed. This forces air/fuel mixture through a central preheating chamber, which completely vaporizes air/fuel mixture. During high speed or heavy load conditions (wide open throttle), secondary throttle plates open to allow air/fuel mixture to enter directly into cylinders without going through preheat chamber.