California and Canada
PRIMARY MAIN SYSTEM
The fuel flowing out of the passages at bottom of float chamber passes through the primary main jet, and is mixed with air coming from main air bleed. The gas mixture is pulled out into the venturi through the main nozzle.
When throttle valve is wide open and engine requires dense mixture gas, power valve opens, and fuel also flows into main system.
IDLING AND SLOW SYSTEM
Passing through the main jet, the fuel passage is separated from main line, fuel flows through the slow jet, primary slow air bleed is ejected from the by-pass hole and idle nozzle.
ACCELERATING MECHANISM
A mechanical accelerating pump synchronized with the throttle valve is used.
When throttle valve is closed, piston rod is pushed up with linkage, which pushes up piston through piston return spring.
When piston comes down, inlet check ball closes, outlet check ball opens, and fuel within the pump is blown out from the pump jet by compressed piston return spring. The fuel hits against side wall of small venturi, becoming minute drops and compensating transient spareness of fuel.
SECONDARY MAIN SYSTEM
When the primary throttle valve is wide open and engine produces high power, the secondary throttle valve begins to open by the diaphragm. Fuel-air mixture produced by the functions of the main jet, main air bleed and emulsion tube, in the same manner as in the primary system, is pulled out through the main nozzle into the venturi. The structure is almost the same as the primary main system.
The secondary throttle valve is linked to the diaphragm which is actuated by the vacuum created in the venturi. A vacuum port is provided at each of the primary and secondary venturis, and the composite vacuum of these ports actuates the diaphragm.
As the linkage causes the secondary throttle valve to close until the primary throttle valve opening reaches approximately 48°, fuel consumption during normal operation is not excessive.
During high speed running, as the vacuum at the venturi is increased, the diaphragm is pulled against the diaphragm spring force, and then secondary throttle valve is opened.
The other side, during low speed running (as the primary throttle valve opening does not reach 48°), the secondary throttle valve is locked to close completely by the locking arm which is interlocked with primary throttle arm by linkage.
When the primary throttle valve opening reaches wider position than 48°, the secondary throttle valve is ready to open, because the locking arm revolves and leaves from the secondary throttle arm.
T.V.V. lets the venturi vacuum leak during cold condition [water temperature below 60°C (140°F)], so that the opening of secondary throttle valve may delay, and thus improve driveability.
SECONDARY SLOW SYSTEM
(STEP SYSTEM)
This system aims at the power filling up of the gap when fuel supply is transferred from the primary system to the secondary system.
HIGH SPEED ENRICHER
The high speed enricher improves high engine output performance during high speed driving. When the velocity of suction air flowing through the carburetor secondary bore increases, additional fuel is drawn out of the enricher nozzle.
Anti-dieseling System
As the ignition switch is turned off, the valve is brought into operation, shutting off the supply of fuel to the slow circuit.
The valve also shuts off fuel when decelerating. Refer to "Fuel Shut-off System".
Float System
There is only one float chamber, while two carburetor systems, primary and secondary, are provided.
Fuel fed from the fuel pump flows through the filter and needle valve into the float chamber. A constant fuel level is maintained by the float and needle valve.
Because of the inner air vent type float chamber ventilation, fuel consumption is not affected by dirt accumulated in the air cleaner.
The top of needle valve is made of special hard steel and will not wear for all its considerably long use. Besides, the insertion of a spring will prevent the flooding at rough road running.
Electric Auto Choke (California & Canada)
An electric heater warms a bimetal interconnected to the choke valve, and controls the position of choke valve and throttle valve in accordance with the time elapsed, the warm-up condition of the engine, and the outside ambient temperature.
1. Electric heater in thermostat cover.
The double stage heating system is provided to obtain an optimum heating capacity. This system consists of first and second stage heater. The first stage heater (A) always operates to heat the bimetal during the time when electric current flows through the auto- choke circuit, and in addition to the first stage operation, the second stage heater (B) begins to operate when the bimetal temperature reaches to the level of about 15°C (59°F) so that the choke valve opens more early. This operation of the second stage heater is controlled by a thermo switch attached to the bimetal.
2. Bimetal
Electric current flows through the heater as the engine starts, and warms the bimetal. The deflection of the bimetal is transmitted to the choke valve through the choke valve lever.
3. Fast idle cam
The fast idle cam determines the opening of the throttle valve so that the proper amount of mixture corresponding to the opening of the choke valve will be obtained. The opening of the choke valve is dependent upon the warm-up condition of the engine.
4. Choke unloader
When accelerating the engine during the warm-up period, that is, before the choke valve opens sufficiently, this unloader forces the choke valve open a little so as to obtain an adequate air4uel mixture.
5. Vacuum break diaphragm
After the engine has been started by cranking, this diaphragm forces the choke valve open to the predetermined extent so as to provide the proper air-fuel ratio.
A two stage-acting type vacuum diaphragm is employed.
Dash Pot System
In automatic transmission models, a dash pot prevents engine stall resulting from quick application of the brake or from quick release of the accelerator pedal after it has been tread upon slightly.