Carburetor: Description and Operation

Fig. 2 Idle circuit schematic:

The 6510-C carburetor used is a staged 2 barrel downdraft carburetor which uses solenoid operated fuel metering and air bleed valves to control air/fuel mixtures in the primary side. The primary side of the carburetor includes 5 systems; conventional float and acceleration enrichment systems, an electrically heated choke, and Mixture Control (MC) solenoid controlled idle and main metering systems. The MC solenoid is an on/off type solenoid, cycled at a fixed rate by the system computer which monitors various sensors in order to determine proper air fuel mixtures for operating conditions. The computer controls air fuel mixtures by varying the solenoid "on" time (dwell period) during each cycle. The secondary side of the carburetor, which draws fuel from the common float bowl, includes conventional main metering and pull over fuel enrichment systems which supplement primary side systems. The secondary throttle is controlled by interconnecting linkage which prevents it from opening until the primary side throttle is almost fully open.

In the primary idle circuit, Fig. 2, fuel flows into the idle fuel well through the main jet, a factory adjusted lean authority orifice and through the solenoid controlled fuel orifice. Fuel is drawn through a calibrated tube into the idle circuit and emulsified by air entering the upper and lower fixed air bleeds and through a cross-channel to the solenoid controlled air bleed. The emulsified fuel is discharged through idle and transition ports, and regulated by a sealed mixture adjusting screw. The MC solenoid controls air/fuel mixtures during idle and transition acceleration by controlling the air bleed and fuel orifice openings.

Fig. 3 Primary main metering circuit schematic:

In the primary main metering circuit, fuel is metered through the main jet, lean authority orifice, and the solenoid controlled fuel orifice, Fig. 3. Air is drawn into the main circuit through a main air bleed and used to emulsify fuel which is discharged through a nozzle in the booster venturi. The MC solenoid controls air/fuel mixtures during off-idle through wide open throttle operation by controlling the opening of the fuel orifice located in the float bowl floor.

Additional carburetor or carburetor mounted controls include a solenoid operated bowl vent valve, throttle position sensor, integral automatic choke with a non-adjustable, electrically heated thermostat, and a Stepped Speed Control (SSC) system. The SSC system consists of a vacuum operated actuator which opens the primary throttle when vacuum is applied, a solenoid controlled Vacuum Control Valve (VCV), and an engine speed sensor. The VCV is held open when energized, applying vacuum to the actuator which in turn opens the throttle a preset amount to prevent stalling or deceleration backfire. The VCV is energized under the following conditions: excessive coolant temperature, during first 10 seconds of engine operation and with A/C compressor clutch engaged on models with A/C; power steering pump output pressure above calibrated pressure; engine speed above calibrated RPM on models with manual transmission.