Operation of carburetors 2105-1107010 (VAZ-2105)

Open large image in new tab »

---

Operation of the carburetor when starting and warming up a cold engine

Due to the low temperature of engine parts and the low speed of air movement through the carburetor, mixture formation is significantly impaired. For reliable engine starting, a strong enrichment of the combustible mixture is required, which is provided by the carburetor starting device.

When starting a cold engine, close the air damper 17 by pulling the control handle towards you until it stops. In this case, the rod 21 will take the extreme left position in the slot of the rack 23, and the rod 4 (see fig. 9), going down, under the action of the rotation of the three-arm lever 30, will turn the lever 6 and slightly open the throttle valve of the first chamber to the required value. In this case, the throttle control pedal must not be pressed in order to prevent excess fuel from being supplied to the engine.

When the engine crankshaft is turned by the starter, the resulting vacuum is transmitted both to the openings of the idle system and through the slightly open throttle valve 40 (see fig. 10) the first chamber to the sprayer of the main metering system. Under the action of the vacuum, the fuel begins to flow intensively from the holes of the idle system and the sprayer. From the holes of the idle system, the fuel comes in the form of a fuel-air emulsion. Air is mixed with the fuel through the air jet 26. At the same time, the vacuum is transmitted through the communication channel with the throttle space to the working cavity of the diaphragm 24 of the starting device, but it is not enough to overcome the resistance of the return spring of the diaphragm. When stable flashes appear, the vacuum increases, the diaphragm 24 with the rack 23 are drawn in, and the rod 21 slightly opens the air damper 17. In this case, the lever 23 (see fig. 9), turning, compresses the spring located in the telescopic rod 24. The starting device, automatically opening or closing the air damper, prevents excessive enrichment or depletion of the mixture.


As the engine warms up, the air damper is fully opened, returning the starting device control handle to its original position. The extreme retracted position of the diaphragm 24 (see fig. 10) is adjusted by screw 25. When the handle of the starting device is fully extended and the rack 23 is acted upon manually, the air damper should open slightly, and the gap between its lower edge and the wall of the inlet neck should be equal to 5.0-5.5 mm. When the air damper is fully closed, the throttle valve of the first chamber should open slightly by 0.7-0.8 mm. This gap is adjusted by bending the rod 4 (see fig. 9).

Carburetor operation at engine idle speed

The throttle valves are closed in idle mode. In this case, the transition holes of the system are located slightly above the upper edge of the valve. The air damper is completely closed. The vacuum from under the throttle valve of the first chamber is transmitted through the holes of the idle system to the channels of the system. Under the action of the vacuum, the fuel entering the emulsion well from the float chamber through the main fuel jet 34 (see fig. 10), rises to fuel jet 33, mixes with air entering through air jet 26, additionally mixes with air entering through transition holes and through the hole adjusted by screw 38, enters seat 39. Then the emulsion passes under needle 37 and through holes in seat 39 into the engine intake pipe. Due to the high speeds of emulsion passage through seat 39, high-quality mixing of fuel and air occurs. In this mode, the vacuum in the small diffuser is insignificant, and fuel from the sprayer of the main metering system does not enter the engine.

Operation of the forced idle economizer

The forced idle economizer shuts off the supply of fuel and air mixture through the idle system in the forced idle mode, i.e. when the vehicle is braking with the engine, when the throttle control 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. At the same time, atmospheric pressure is created in the working cavity of the forced idle economizer and needle 37, connected to the economizer diaphragm, closes the outlet of the fuel-air emulsion, thereby eliminating the emission of carbon monoxide (CO) into the atmosphere and simultaneously reducing fuel consumption. The change in the working cavity of the vacuum to atmospheric pressure and vice versa is carried out by an electro-pneumatic valve, which is connected by a hose through pipe 61 (see fig. 9) with the working cavity of the economizer. The electro-pneumatic valve is triggered by microswitch 32 or an electronic control unit connected in parallel to the microswitch. At a crankshaft speed of 1600-1680 min'1, the electronic unit is switched off, but the electro-pneumatic valve remains open due to the switched on microswitch. In the forced idle mode, the throttle valves are abruptly closed, lever 1 presses the lever of microswitch 32 and switches it off, the electro-pneumatic valve closes, and the working cavity of the forced idle economizer communicates with the atmosphere. In this case, needle 37 (see fig. 10) economizer closes the outlet of the idle system and the outlet of the fuel-air mixture. When the crankshaft speed decreases to 1200-1260 min⁻¹ the electronic unit switches on the electro-pneumatic valve and a vacuum is created in the working cavity of the economizer, while the needle 37 is pulled back, the supply of the fuel-air mixture begins and the engine starts working again.

Carburetor operation in throttle modes

In throttling modes, the first mixing chamber mainly operates. The required composition of the combustible mixture is ensured by the joint operation of the main metering system and the idle system. As the throttle valve of the first chamber opens, the vacuum in the atomizer increases, the fuel in the emulsion well rises and, upon reaching the holes of the emulsion tube 35, is captured by air entering through the jet 19 and is drawn into the atomizer. The vacuum in the mixing chamber is sufficient, so the fuel also comes from the holes of the idle system. The fuel consumption of both systems is limited by the main fuel jet 34.

When a certain vacuum is reached in the mixing chamber, the throttle valve of the second chamber begins to open due to the retraction of the diaphragm and the rod of the pneumatic drive connected to the lever of the throttle valve of the second chamber. Fuel also begins to flow out of the sprayer of the main metering system of the second chamber. The absence of dips in the engine operation at the moment of the beginning of the opening of the throttle valve of the second chamber is ensured by the holes 44 of the transition system, which comes into operation from this moment. Subsequently, the second chamber operates similarly to the first.

Carburetor operation at maximum engine power

In the maximum power mode, the throttle valves of both chambers are fully open: the main metering systems, the idle system, the transition systems, and also the economizer, when the required vacuum is reached, operate.

Due to some reduction in the vacuum in the channels of the idle system and the transition system with fully open throttle valves, the fuel outflow from these systems is insignificant. When sufficient vacuum is achieved in the small diffuser of the second mixing chamber, the economizer comes into operation, enriching the combustible mixture at full load. Fuel from the float chamber enters through the economizer jet 8, mixes with air coming from the jet 6, and then through the emulsion jet 10 and the sprayer 11 is sucked into the mixing chamber.

Operation of the accelerator pump

The accelerator pump operates in the engine load increase mode; in this case, the necessary enrichment of the mixture is achieved by injecting an additional portion of fuel into the air flow of the first mixing chamber.

With a sharp increase in load (the throttle valve opens abruptly) the cam of the accelerator pump drive on the valve axis acts on the lever 1, which compresses the spring placed inside the telescopic cup of the working diaphragm 49. When released, the spring moves the diaphragm, providing a smooth, drawn-out injection of fuel through the sprayer 15. The profile of the cam of the accelerator pump provides a double injection, the second injection occurs at the beginning of the opening of the throttle valve of the second chamber.

Operation of the pneumatic drive of the second chamber throttle valve

At low engine loads, when the throttle valve of the first chamber is slightly open, the vacuum in the diffusers is insufficient to operate the pneumatic drive, and under the action of the spring, the pneumatic drive rod is lowered. As the load increases and the throttle valve of the first chamber opens, the vacuum in it increases and at a certain point leads to the movement of the diaphragm mechanism up to its full stroke with simultaneous twisting of the spring on the axis of the throttle valve of the second chamber. However, the throttle valve of the second chamber remains closed until the throttle valve of the first chamber is opened to an angle of approximately 48°. With the throttle valve of the first chamber fully open and a large air flow (high crankshaft speed) the throttle valve of the second chamber opens completely. The position of the throttle valve of the second chamber is adjusted automatically depending on the engine speed.

When the vehicle speed decreases (with the first chamber throttle valve fully open at all times) the engine crankshaft speed decreases, the vacuum in the diffusers decreases, and the throttle valve of the second chamber closes. This improves mixture formation in the first chamber.

When the throttle valve of the first chamber is abruptly closed, the throttle valve of the second chamber is also forcibly closed. Jets 51 and 52 eliminate possible oscillation of the pneumatic drive mechanism.