MODELS 2G-2GC-2GV PAGE 10

Delco

purpose of the main well inserts is to break up vapor bubbles which may form in the main well during hot engine operation. This prevents the vapor bubbles in the fuel, caused by heat, from disrupting carburetor metering and provides even fuel flow from the main well tubes and discharge nozzles. The main well inserts are used on applications where engine heat causes excessive vapor bubbles in the main well area. Some applications use plastic main well inserts added to the main well area for improved fuel control in the off-idle, transfer and part throttle range of operation to aid in exhaust emission reduction.

enrichment to the main metering system at higher air flows. These feed holes connect directly to the fuel in the float bowl through channels that lead directly into a tube that extends into the fuel just above the main metering jets. At approximately 8 pounds of air flow per minute and above, the fuel begins to feed from these discharge holes to supplement fuel flow from the main metering system.

POWER SYSTEM

POWER SYSTEM (EXCEPT VEGA MODELS) (Fig. 13)

LOWER IDLE AIR BLEEDS (See Figure 11)

Lower idle air bleeds are used in some 2-bore carburetor applications to act as supplementary fuel feeds after off-idle, and during the main metering and power system operation. As the throttle valves are opened further past the off-idle discharge holes, air velocity past the lower idle air bleeds creates a vacuum and they begin to feed fuel. They continue to supply fuel during the main metering and power system operation, where they supplement fuel flow from the main discharge nozzles.

The purpose of the lower idle air bleeds is to supply additional fuel, to mix with the air, during the period when the off-idle discharge holes cannot meet the fuel demands and the main discharge nozzles have not begun to feed sufficient fuel.

The lower idle air bleeds draw fuel through the idle system. Engine demands determine whether or not these supplementary fuel feeds are used in a particular carburetor model.

PULL-OVER ENRICHMENT (Fig. 12)

The power system in the Rochester 2-bore carburetor provides extra mixture enrichment to meet power requirements under heavy engine loads and high-speed operation. The richer mixtures are supplied through the main metering system. The spring-loaded power piston, located in the cavity in the air horn, directly above the power valve, is held in the up position by engine manifold vacuum supplied directly through a connecting passage from the base of the carburetor. The power system is exposed to manifold vacuum at all times during engine operation.

During idle and cruising ranges, the relatively high engine vacuum holds the power piston in the up position against tension of a calibrated spring located on the power piston stem. During this period, the power valve remains closed.

Increases in engine load lower the manifold vacuum. When it has dropped sufficiently, the power piston spring overcomes the upward vacuum pull and the power piston moves downward, opening the power valve to allow additional fuel to flow through the calibrated restrictions and on into the main well area. The fuel flowing through the power system supplements the fuel passing through the main metering jets to give the proper mixtures required for power operation.

FIGURE 12

A pull-over enrichment circuit is used on some late large bore 1-1/2" 2GC-2GV carburetors to add fuel enrichment at higher engine speeds. As a result, leaner mixtures can be maintained during the part throttle or cruising ranges for improved exhaust emission control. The pull-over enrichment circuit uses two additional feed holes, located in the air horn just above the choke valve, that provide sufficient