Carburetor operation 21051-1107010 (VAZ-2105)

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Operation of the carburetor when starting and warming up the engine

The necessary enrichment of the combustible mixture is provided by the carburetor starting device.

When starting a cold engine, the air damper control handle is pulled out to the stop. The throttle control pedal is not touched in order to prevent an uncontrolled excess portion of fuel from being supplied to the engine. In this case, the air damper control lever 52 turns counterclockwise, the expanding groove releases the air damper lever pin and the damper is held in the closed position by the return spring. The outer edge of the lever 52 presses the adjusting screw 50 for opening the first chamber throttle valve, as a result of which the lever 51 opens the first chamber throttle valve to the required value. When the crankshaft is turned by the starter, the resulting vacuum is transmitted to the openings and channels of the idle system and to the sprayer 10 of the main metering system. Under the action of the vacuum, the fuel will intensively flow out of the openings of the idle system and the main metering system. At the same time, a vacuum is created in the working cavity of the diaphragm 2 of the trigger, but it is insufficient to overcome the resistance of the return spring. At the moment of the appearance of flashes, the vacuum increases, under the action of which the diaphragm 2 with the rod 3 are drawn in and the rod 3 opens the air damper 9 slightly by the lever pin.

The air damper opens or closes automatically when the engine starts and warms up, preventing excessive enrichment or leaning of the mixture. As the engine warms up, the air damper is fully opened by returning the air damper control handle to its original position.

Carburetor operation at idle speed

In the idle mode, the throttle valve 36 is closed, while the slot 37 of the transition system of the first chamber is above the upper edge of the valve. The air valve is fully open. The vacuum through the idle hole, covered by the mixture quality adjusting screw 38, is transmitted to the idle system channels and to the fuel jet 5. Under the action of the vacuum, the fuel entering the emulsion well through the main fuel jet 42 rises to the fuel jet 5, partially mixes with the air entering through the air jet 7, is mixed a second time with the air entering through the slot 37 of the transition system, and in the form of an emulsion enters under the adjusting screw 38 into the throttle space.

The vacuum in the small diffuser is insufficient and fuel does not flow from the sprayer 10 of the main metering system.

To regulate the engine operation at idle, there is an adjusting screw for the amount of mixture, which regulates the amount of opening of the throttle valve of the first chamber, and an adjusting screw 38 for the quality (composition) of the mixture.

Operation of the forced idle economizer

The forced idle economizer shuts off the fuel supply through the idle system when the engine is in forced idle mode (when the vehicle is braking with the engine, when the throttle pedal is released and the clutch is not disengaged). In the forced idle mode, the throttle valves are closed and the crankshaft speed exceeds the idle speed.

The economizer includes a limit switch mounted on the idle mixture quantity adjusting screw, electromagnetic shut-off valve 4, electronic control unit and electrical wires for connecting instruments. The economizer will operate only when the throttle control pedal is released, when the limit switch is connected to ground. In this case, the throttle actuator lever 51 will rest against the limit switch and close it to ground. During cold engine starting, the limit switch will not be connected to ground, since the throttle valve will be slightly open.

The electronic control unit supplies power to the windings of the electromagnetic shut-off valve 4 until the crankshaft speed at forced idle speed increases and does not exceed 2100 min'1. At a higher speed, the power supply to the valve winding stops and valve 4 shuts off the fuel supply. When the crankshaft speed decreases to 1900 min'1, the control unit again supplies power to valve 4, the fuel supply is resumed and the engine enters idle mode.

To obtain information about the crankshaft speed, the electronic control unit is connected to the ignition coil.

Carburetor operation in throttle modes

The first mixing chamber operates mainly, which ensures engine operation in a wide range. At the same time, the required composition of the combustible mixture is ensured by the joint operation of the main metering system of the first chamber and the idle system with the transition system.

As the throttle valve of the first chamber opens, the gap 37 of the transition system is subject to vacuum and ceases to operate as an air jet. The fuel-air mixture also begins to flow through it. As the throttle valve opens further, the vacuum in the sprayer 10 increases, the fuel in the emulsion well begins to rise, and upon reaching the holes in the emulsion tube 43, it is captured by air flowing through the sprayer 6 and is drawn into the sprayer. From this point on, these systems begin to work together.

Operation of the power mode economizer

The economizer eliminates fluctuations in the qualitative composition of the fuel in the combustible mixture during suction pulsation, and also enriches the combustible mixture when the vacuum decreases with a significant opening of the throttle valves.

The mixture is sucked into the engine intermittently, its pulsation will be stronger, the lower the engine crankshaft rotation frequency. The pulsation is also transmitted to the sprayers of the main dosing systems. This reduces the efficiency of automatic control of the mixture composition by the main dosing system.

The economizer operates at a certain vacuum under the throttle valve 36. The ball valve 24 is closed while the diaphragm 21 is held by the vacuum. When the vacuum decreases, the valve 24 opens under the action of the spring. The fuel will flow through the ball valve into the emulsion well of the first chamber. This fuel will be drawn into the atomizer 10, equalizing the composition of the combustible mixture during suction pulsation. The economizer will also enrich the combustible mixture at a low vacuum under the throttle valve 36.

Carburetor operation at maximum engine power

After the throttle valve of the first chamber opens to 2/3 of its size, lever 37 (fig. 11) the throttle valve of the second chamber will be forced to open. Both valves come to the fully open position simultaneously. The absence of dips in operation is ensured by holes 32 (see fig. 12) transition system of the second chamber.

When the throttle valves are fully open, the vacuum in the channels of the idle system and transition systems drops, and in the small diffusers and sprayer 13 of the economizer it increases, as a result of which the fuel-air mixture intensively flows out of sprayers 10 and 13, enriching the combustible mixture. Due to the presence of air jets 6 and 13, which have large flow sections, as well as large flow sections of sprayers and channels, the vacuum in the emulsion wells still remains less than the vacuum at the outlet openings of transition systems 32, 37 and the idle system. Therefore, the idle system and transition systems operate as fuel systems and the mixture does not become too lean. However, the amount of fuel supplied in this mode through the above-mentioned systems is insignificant.

Operation of the accelerator pump

Enriches the combustible mixture during acceleration of the vehicle. The accelerator pump injects an additional portion of fuel into the air flow passing through the carburetor. Fuel enters the working cavity of the pump from the float chamber through the check ball valve 45. When the throttle valve is opened sharply, the cam 54 acts on the lever 47, which compresses the spring in the telescopic cup of the diaphragm 46. When released, the spring smoothly moves the diaphragm, which ensures a prolonged injection of fuel through the channel into the valve and then through the sprayers 11 into both mixing chambers.

The source is on the website: www.VAZbook.ru

Cam 54 has a special profile that provides double injection. Moreover, the second injection coincides with the beginning of the opening of the throttle valve of the second chamber.