Carburetor: Description and Operation

Fig. 1 Mikuni non-feedback carburetor assembly:

1984 CALIFORNIA MODELS
The Mikuni non-feedback carburetor, Fig. 1, is a conventional downdraft two barrel compound type carburetor. The automatic choke on these units is of the thermo-wax type which is controlled by engine coolant temperature. The main body on these units consists of a black resin compound. Other features of these units include a diaphragm type accelerator pump, bowl vent, fuel cut-off solenoid, [1][2]air switching valve, sub EGR valve, coasting air valve and jet air control valve. California units also incorporate a high altitude compensation system.

Fig. 2 Mikuni feedback carburetor assembly:

1984 EXC. CALIFORNIA MODELS & ALL 1985
The Mikuni feedback carburetor, Fig. 2, is a two barrel down draft carburetor designed for electronic fuel control and closed loop operation.
With a closed loop system of mixture control, this carburetor provides optimum air/fuel control during all ranges of engine operation. Fuel metering is accomplished through the use of three solenoid valves that reduce or add fuel to the engine.
The fuel flow through the valves is controlled by the length of time electrical current is supplied to the solenoids. The solenoids operate at a fixed frequency generated by the electronic control unit. By varying the amount of time that the solenoid is energized during each duty cycle, the air/fuel mixture delivered to the engine can be precisely controlled. The duty cycle applied to the solenoid is controlled by the electronic control unit in response to signals received from various sensors.
There are eight basic systems in the feedback carburetor: fuel inlet, primary metering, secondary metering accelerator pump, choke, jet mixture, enrichment and fuel cut-off. The first five systems are basically the same as those on the non-feedback carburetor while the last three are unique to the feedback carburetor.