Throttle Plate - Carb.: Description and Operation

Fig. 3 Carburetor secondary progression system:

Operation
This system is similar to the primary main metering system.
- When the primary throttle plate is opened approximately 45°, the secondary throttle plate begins to open, Fig 3.
- The air/fuel mixture begins flowing from the secondary transfer holes as they are exposed to manifold vacuum.
- As the throttle plates are opened further, the secondary main metering system begins to operate.