To increase the horsepower and torque capability of an engine, the mixture supplied by the main fuel system is supplemented by an additional quantity of air-fuel mixture from the secondary fuel system on a driver demand basis. The secondary throttle plates are mechanically connected to the primary throttle lever. The secondary throttle plates begin to open when the primary throttles are 3/4 open and the engine is warmed sufficiently to disengage the secondary throttle lockout lever.
The secondary throttle lockout prevents the secondary throttles from opening during cold engine, wide-open, throttle operation. Offset air valve plates are located above the secondary main venturis and below the booster venturis. A calibrated spring preloads the air valve plates to a closed position. When the secondar throttle plates begin to open, manifold vacuum appears below the air valve plates.
Enrichment discharge tubes, located in the secondary main venturis below the air valve plates, sense the pressure drop and start the fuel flow in the secondary fuel system. The air valve plates also react to the pressure drop and start to open. The amount of opening is controlled by the velocity of air acting upon the offset plates and by the opposing torque exerted by a spiral torsion spring that is connected to the air valve plate shaft. An integral hydaulic dashpot dampens sudden movements of the air valve plates to prevent flutter and erratic engine operation.
The secondary throttle plates are linked to the primary throttle lever by the secondary operating link. The secondary throttle plates begin to open when the primary throttle plates are 3/4 open, provided the engine has warmed sufficiently to disengage the secondary throttle lock-out. The secondary throttle lock-out prevents the secondary throttle plates from opening during cold engine, wide-open throttle operation. An air valve plate is located in the upper body above the secondary throttle plates. The air valve plate is held in the closed position by a calibrated spring. When the secondary throttle plates begin to open, manifold vacuum appears below the air valve secondary main metering jets, located just below the air valve plate, sense the pressure drops, and fuel begins to flow through the secondary fuel system.
The air valve also reacts to the pressure drop and begins to oepn. THe amount of opening is controlled by air flowing through the secondaries and by the opposing force of the air valve spring. The amount of fuel flowing through the secondary metering system is controlled by the secondary metering jets and the secondary metering rods. The secondary metering rods are connected to the air valve so that the size of the main metering jets and the corresponding fuel flow is in direct proportion to the air valve opening and the volume of air required to produce the opening.
In addition, an integral hydraulic piston dampens sudden movement of the air valve to prevent flutter and erratic engine operation.
When the primary throttle plates begin to close on deceleration, the secondary throttle plates are closed mechanically. As air flow through the secondaries diminishes, the air valve plate is closed by the force of the air valve spring.