Holley 2300C, 4160, 4160C carbs


			the strength of the vacuum. This in turn, is deter mined by the air-flow through the bores to the engine. As the air-flow increases, a greater sec ondary throttle plate opening will result and the secondary bores will supply a greater portion of the engine's requirements.As top speed is reached, the secondary throttle plates will approach wide open.

			The bleed past the ball check valve in the vacuum passage of this carburetor limits the rate at which the secondary throttle plates are allowed to open. Any rapid increase in vacuum, which would tend to open the secondary throttle plates too suddently, merely holds the ball check valve securely against its seat. The opening of the throttle plates is slowed to a rate governed by the amount of air passing through an air bleed in the check valve seat. On some units this bleed is a groove in check ball seat. On other units this is a drilled by pass. This allows the vacuum to build up comparatively slowly at the diaphragm which results in a controlled rate of opening for the secondary throttle plates. As the secondary throttle plates begin to open, a vacuum is created in the secondary bores, first at the throttle plates and then, as air flow increases, at the throat of the secondary venturi. This vacuum assists the sec ondary metering system to operate.


		Secondary Throttle Operating System		When engine speed is reduced, venturi vacuum in the bores become weaker. The momen tarily stronger vacuum at the secondary throttle operating diaphragm moves the ball check valve off its seat in the vacuum passage, permitting an immediate flow of air into the diaphragm chamber. As the vacuum acting on the diaphragm is lessened, the load on the diaphragm spring will commence closing the secondary plates. The diaphragm spring is assisted by the design of the secondary plates. Each secondary plate is slightly offset. When the plates are closing, the combined force of manifold vacuum and the air stream has greater effect on the larger, upstream area of the plates, forcing the plates to a closed position. The secondary plates are retained in the closed posi tion when the primary plates are fully closed by the secondary throttle connecting rod. This rod, which is fastened to the primary throttle lever, rides in a slot in the secondary throttle lever.

3. ACCESSORIES

	A. SECONDARY THROTTLE OPERATION

(1) VACUUM - All four barrel carbure tors except 4160 with Mechanical Secondarys.

At lower speeds, the secondary throt tle plates remain nearly closed, allowing the engine to maintain satisfactory fuel-air ratios and distribution. When engine speed increases to a point where additional breathing capacity is needed, the vacuum controlled secondary throttle plates begin to open.

Vacuum taken from one of the primary bores and one of the secondary bores acts upon a diaphragm which controls the secondary throttle plates. On Model 4150-G the two pick-up ports are located in the primary barrel only. At high speeds when engine requirements approach the capacity of the two primary bores, the increased primary venturi vacuum moves the diaphragm, compres sing the diaphragm spring. The diaphragm, acting through the diaphragm link and lever, will com mence to open the secondary throttle plates. The position of the secondary throttle plates depends on

				(2) MECHANICAL - MODEL 4160 WITH MECHANICAL SECONDARYS - The secondary throttle plates on this carburetor are connected by linkage to the primary throttle linkage and are mechanically operated.

				As the primary throttle plates con tinue to open as accelerator pedal pressure is