9D-3 MODELS 2G-2GC-2GV PAGE 11

A hole is drilled from the carburetor air horn to the bore of the power piston cavity to break any vacuum that might leak around the sides of the power piston. The purpose of the vacuum break hole is to prevent the transfer of vacuum from the piston to the top of the fuel in the float bowl. Any vacuum acting on the fuel in the float bowl will affect carburetor calibration.

In operation, vacuum (low pressure) from the carburetor venturi is transmitted through the main discharge nozzle to the main fuel well. The power system passage, being open to the main well area, also receives this vacuum signal. At a predetermined point, when extra fuel enrichment is needed for power and high speed, a check valve in the power valve assembly is lifted off its seat. Fuel then flows from the float bowl through a calibrated hole in the power valve assembly. The fuel then passes upward forcing a piloted check valve off its seat and then on into a cavity at the top of the power valve. The fuel then flows downward through a channel in the power valve assembly and then into the power valve cavity in the float bowl. It then passes on through separate fuel channels with calibrated restrictions into the main fuel wells.

The power valve (See inset), installed in the bottom of the float bowl, consists of a plunger and closing spring. When manifold vacuum drops to a predetermined point (called "power cut-in") dependent upon engine load and throttle opening, the power piston moves downward under spring tension to force the power valve plunger off its seat. Then, fuel flows through the valve on into separate fuel channels passing through calibrated restrictions, by-passing the main metering jets, and then on into the main well.

NOTE: On some models, power restrictions are not used in the float bowl assembly and metering of fuel for power mixtures is controlled by the inlet orifice of the power valve assembly.

Some applications use a two-step power valve. The first step unseats the plunger and fuel is metered by the plunger for light power requirements. For the second step, the plunger is bottomed completely and the fuel is metered entirely by the power restrictions for full power operation.

At this point, the fuel from the power system supplements the fuel passing through the main metering jets into the fuel wells and passes up the main discharge nozzles and out into the boost venturi. The extra fuel added by the power system gives the desired enrichment for power operation.

POWER SYSTEM (VEGA MODELS) (Fig. 14)

The power enrichment valve assembly cannot be disassembled so a thorough cleaning is necessary to make sure the valve inside the assembly is clean and free of foreign material.

The power system on all 2G, 2GC, 2GV models is specifically calibrated for a particular engine's power requirements and requires no adjustment in the field.

ACCELERATING PUMP SYSTEM (Fig. 15)

FIGURE 14

On 2GV models for Vega 4-cylinder engines, the conventional vacuum-operated power piston is not used and is replaced by a power enrichment valve assembly. The power enrichment valve is installed in the bottom of the float bowl which contains an inlet channel feeding fuel into the power valve cavity.

The purpose of the power enrichment valve system is to provide additional fuel for power and high-speed requirements to the engine, and supplements the main metering system.

FIGURE 15

The power enrichment valve system operates as follows:

Power mixtures are controlled by air velocity past the boost venturi whereby fuel is added for power enrichment according to engine demands.

During quick acceleration when the throttle is opened rapidly, the air flow and manifold vacuum change almost instantaneously, while the heavier fuel tends to lag behind