lawn mowers, like all gasoline powered tools for the garden, are not difficult to maintain. It is possible and necessary to repair, configure yourself. For example, adjusting the carburetor of the lawn mowers with your own hands is a matter of five minutes.
Lawn mowing carburetor is a unit in the power system. In it, like any carburetors, there is a process of mixing air and fuel (gasoline) for further supply to the engine cylinders.
The main problems and malfunctions of the carburetor.
Strainer There are only two problems with this element:
In order to find out the cause of the breakdown, the fuel filter cover is unscrewed to remove the strainer. If dirt has simply accumulated on it, washing with gasoline or blowing will help.
With visible damage to the strainer, it is imperative to install a new one. There may also be damage on the fuel supply pipe (during repair, check this element).
The carburetor starter in most cases does not function due to blockages. Use acetone or the same gasoline for flushing.
Blowing off carburetor parts with a blockage of compressed air is an acceptable and convenient repair practice.
The device of the carburetor lawn mowers
The basis of the carburetor of the lawn mowers is an aluminum case. It has a diffuser (hole with internal contours). Air is blown through this hole. The oxygen (air) flow rate depends on the cross-section (passage opening) of the diffuser.
The diffuser is equipped with fuel channels. Of these, fuel is drawn in using an air stream.
Outside the carburetor is installed:
- fuel pump;
- jet system;
- fuel / air mixture control system;
The principle of the carburetor lawn mowers
The throttle valve determines the amount of air for supply, and engine power directly depends on this.
Fuel is sucked into the carburetor system by a pump (its membrane). Then it passes through the fitting in the carburetor. Further, the fluid moves through the inlet and outlet valves of the pump. Filtered by mesh. The needle valve moves into the membrane chamber.
Phased operation of the device:
- Air supply to the tube with an air baffle (damper). The partition controls the intensity of the air flow.
- The fuel supply system must be narrowed by a diffuser to increase the flow rate.
- Gasoline through the float chamber and nozzle tube with narrowing. A camera with a float adjusts the temporary volume of gasoline. In the float chamber, the pressure level is neutral, and in the tube with narrowing is already low. Due to the pressure drop, fuel enters through the nozzle.
- The acceleration of the air flow contributes to the transfer of fuel (gasoline) and its atomization. As a result, an air-fuel mixture of the necessary proportion or density is formed.
- The air-fuel mixture enters the engine cylinder through the fuel pipe.
Dear friends, in this manual we will try to explain on fingers the basic principles of operation of any carburetor, about its structure, with illustrations and fairly detailed comments. This article will be especially useful for beginners who want to understand the topic. In the article we will consider the following points:
The engine operating modes and the composition of the combustible mixture, the idle system and the transition system, the device of the float chamber and the principles of its operation, the main metering system of the carburetor, the start-up system, the principle of operation of the econostat and much more. Indeed, the appetite of your car directly depends on the proper operation of all these nodes. It can be either higher or lower than that indicated in the technical specifications of your machine. For example Vaz expenses. 2114, 2110, 2112 you can find out by clicking on the link, passport costs of the seven VAZ-2107 you can look here , etc. In general, be patient, popcorn and get ready for interesting reading.
Modes of operation of the engine and the composition of the combustible mixture
COMPOSITION OF FUEL MIXTURE For the operation of the internal combustion engine, a mixture of fuel with air is necessary. In carburetor engines, fuel (gasoline) is mixed with air in a certain proportion outside the cylinders and, partially evaporated, forms a combustible mixture. This process is called carburetion, and the device preparing such a mixture is called a carburetor. The mixture, passing through the inlet pipe, enters the engine cylinders, where it mixes with the remains of hot exhaust gases, forming a working mixture. Particles of atomized fuel evaporate. To start the engine and its operation in different modes, you need a different composition of the combustible mixture. Therefore, the carburetor is designed so that it allows you to change the quantitative ratio of atomized fuel and air in the mixture entering the engine cylinders. For complete combustion of 1 kg of fuel, about 15 kg of air is needed. The air-fuel mixture in this proportion is called normal. The engine operating mode on this mixture has satisfactory performance in terms of economy and developed power. A slight increase in the amount of air in the air-fuel mixture compared to its normal content (but not more than 17 kg) leads to a depletion of the mixture. On a lean mixture, the engine runs in the most economical mode, i.e. fuel consumption per unit of developed power is minimal. The engine will not develop full power on such a mixture. With an excess of air (17 kg or more), a poor mixture is formed. The engine on such a mixture is unstable, while the fuel consumption per unit of generated power increases. On a mixture overpriced, containing more than 19 kg of air per 1 kg of fuel, engine operation is impossible, since the mixture is not ignited by a spark. A small lack of air in the air-fuel mixture compared to normal (from 15 to 13 kg) contributes to the formation of an enriched mixture. This mixture allows the engine to develop maximum power with a slightly increased fuel consumption. If the air in the mixture is less than 13 kg per 1 kg of fuel, the mixture is rich. Due to a lack of oxygen, the fuel does not burn completely. A rich mixture engine runs in uneconomical mode, intermittently and does not develop full power. A re-enriched mixture containing less than 5 kg of air per 1 kg of fuel does not ignite. engine operation on it is impossible. STARTING THE ENGINE When starting a cold engine, part of the sprayed fuel settles on the walls of the inlet pipe, and part of the evaporated fuel, once in the cylinders, condenses on the walls. In addition, at low air temperatures, mixture formation worsens, since the evaporation of gasoline slows down. Therefore, to start a cold engine, it is necessary that the carburetor prepare a re-enriched air-fuel mixture. IDLING At idle, the engine speed is low, and the carburetor throttles are almost completely closed. Because of this, the ventilation of the cylinders is not so effective, compared with the work at medium and high frequencies of rotation of the crankshaft and the amount of combustible mixture entering the engine is small. The working mixture contains a large amount of exhaust (residual) gases. Therefore, for stable operation of the engine at idle, an enriched mixture is necessary. PARTIAL LOAD MODE In partial load mode, the engine does not require full power. The throttle valves are not fully open, but the ventilation of the cylinders is good. Therefore, in this mode, a sufficiently depleted combustible mixture. The ratio of the power developed by the engine to the amount of fuel consumed allows us to consider the partial load mode as the most economical. FULL LOAD MODE At full load, the engine requires maximum or close to maximum power. At the same time, the engine runs at high speeds, and the throttle valves are fully (or almost completely) open. This mode requires an enriched mixture with an increased combustion rate. LOAD SHIFT MODE When the engine is operating in a mode of a sharp increase in load, for example, when accelerating a car, an enriched mixture is necessary. But since the process of mixture formation has a certain inertness, in order to prevent the occurrence of a “dip” in speed gain, an additional short-term enrichment of the combustible mixture is required. For this, additional fuel is injected directly into the mixing chamber of the carburetor.
BASIC CARBURETOR SYSTEMS
Modern carburetors are equipped with a dozen different systems and devices that have an extensive network of channels, numerous calibrated holes, sophisticated linkages and pneumatic chambers. It’s not easy to understand this intricate right away. Therefore, it is useful to consider all the main systems separately by the example of simplified schemes. And you should start with the principle of operation and the simplest carburetor device.
The simplest carburetor design
For the gasoline engine to work, it is necessary to add fuel to the intake air, which then burns in the cylinder during the piston stroke. In order for the fuel to reliably ignite and completely burn out, it is necessary to mix it thoroughly with air and at the same time maintain the optimal composition of the combustible mixture in all engine operating modes. These functions are performed by a carburetor connected by an inlet pipe-wire to the engine cylinders. The simplest carburetor consists of two chambers: float and mixing. The process of preparing a combustible mixture continues along the entire path of the fuel and air along the intake path, up to the cylinders, but begins with the atomization of the fuel in the mixing chamber of the carburetor. For this, a tube-shaped atomizer is installed in the mixing chamber. A section of the tube is brought out to the center of the chamber diffuser. The diffuser is the narrowing section of the mixing chamber. The air velocity in the diffuser increases, and a rarefaction occurs in the atomizer. Under the influence of this vacuum, fuel flows out of the atomizer and is intensively mixed with air. Fuel enters the atomizer from the float chamber with which it is connected by a channel. A nozzle is installed in the channel — a plug with a through hole of certain sizes and shapes. The nozzle limits the flow of fuel to the atomizer. One of the conditions for the carburetor to operate normally is the correct setting of the fuel level in the float chamber. The fuel level in the chamber is maintained using a float mechanism with a needle valve. Fuel is supplied to the float chamber through a fuel wire. As the chamber fills, the float rises, and the needle closes the valve opening, while the air displaced by the fuel is discharged out through a special hole. The float chamber and atomizer are interconnected vessels. The fuel level in the float chamber is set so that it is just below the spray tip. At a higher level, the fuel will exit the atomizer, re-enriching the mixture, while at a lower level, the flow of fuel into the atomizer is not enough, resulting in a very depleted fuel mixture. In order to change the composition of the mixture, an air damper is installed in the mixing chamber above the diffuser. As the air damper closes, the mixture will enrich. Excessive covering of the shutter will over-enrich the mixture and stop the engine. To adjust the amount of air-fuel mixture entering the cylinders, a throttle valve is installed in the lower part of the mixing chamber. When the air and throttle flaps are fully open, resistance to air flow is minimal. The simplest carburetor prepares a fuel mixture of the optimal composition only in a certain range of crankshaft rotational speeds. The range depends on the capacity of the nozzle, the cross-section of the diffuser, the fuel level and the position of the throttle. A car engine must operate over a wide range of crankshaft speeds and with constantly changing loads. To prepare a mixture of the optimal composition in all possible operating modes, car carburetors are equipped with additional systems.
Video: The device and operation of the carburetor benzotrimmer
Main dosing system
The main carburetor dosing system is designed to supply the main amount of fuel in all engine operating modes, except for idling. At the same time, at medium loads, it should ensure the preparation of the required amount of lean mixture of approximately constant composition. In the simplest carburetor, as the throttle opens, an increase in the flow rate of air passing through the diffuser is slower than an increase in the flow rate of fuel flowing from the atomizer. The combustible mixture becomes rich. To avoid over-enrichment of the mixture, it is necessary to compensate for its composition with air, depending on the degree of opening of the throttle. In the carburetor, such a compensation is carried out by the main dosing system. In Solex carburetors, compensation is carried out by pneumatic braking: fuel does not enter the atomizer directly from the float chamber, but through the emulsion well — a vertical channel in which the emulsion tube is installed. The walls of the tube have openings for the exit of air entering into it from above through an air nozzle. The flow of fuel into the emulsion well is determined by the fuel jet. In an emulsion well, fuel is mixed with air leaving the openings of the emulsion tube. As a result, the fuel emulsion, rather than clean fuel, enters the atomizer. As the throttle valve opens in the diffuser, the vacuum increases and the outflow of the emulsion from the spray increases. At the same time, the flow of air into the emulsion well increases through the air nozzle, which decreases the flow of fuel from the float chamber through the fuel nozzle. The amount of fuel passing through the nozzle corresponds to the amount of air entering the diffuser, which provides compensation for the composition of the mixture. The required composition of the combustible mixture is determined by the selection of flow sections of the fuel and air jets, as well as the type of emulsion tube.
BALANCED FLOAT CAMERA
In the simplest carburetor, the float chamber is connected to the atmosphere through an opening in the lid. During operation, as the air filter becomes dirty in the diffuser of such a carburetor, vacuum will increase and, therefore, the mixture will begin to enrich. To exclude the effect of air filter pollution on the composition of the combustible mixture, the internal cavity of the float chamber is connected by a channel to the neck of the carburetor.
Idle system and transition system
For. engine idling with a minimum crankshaft speed requires a small amount of combustible mixture. Therefore, the throttle should be almost completely closed. In this case, the vacuum in the diffuser is not enough for the main dosing system to enter into operation. Therefore, the carburetor is additionally equipped with an idle system that prepares the air-fuel mixture in an amount that ensures stable engine operation with the throttle closed. The channels of the idle system connect the throttle space (cavity of the inlet pipe) with the emulsion part of the mixing chamber. When the engine is idling, a high vacuum is generated under the throttle. Under the action of rarefaction, fuel from the emulsion well passes into the idle fuel channel, where it is mixed with air flowing through the air channel from the top of the mixing chamber. The ratio of fuel and air in the emulsion is determined by the throughput of the fuel and air jets that are installed in the idle channels. Next, the emulsion enters the throttle space, where it is mixed with air passing through the gap between the chamber wall and the damper. The clearance is adjusted with the “quantity” stop screw (SOLEX). The amount of fuel emulsion passing through the channel into the backspace is regulated by a cone-shaped screw (“quality” screw). When the screw is screwed, the passage section of the channel decreases. And vice versa. With a smooth opening of the throttle, the air flow through the mixing chamber increases, and the amount of incoming emulsion remains at the same level. The vacuum in the diffuser is still not enough for the main dosing system to enter into operation. As a result, the mixture is leaner and a “failure” is observed in the engine. To ensure a smooth transition from idle to medium load, a transition system is used, which is combined with an idle system. The transition system channel connects the emulsion channel of the idle system with the over-throttle space of the mixing chamber. The outlet of the channel is located in such a way that, after opening the throttle, it is in the rarefaction zone; through it, an additional amount of emulsion enters the mixing chamber, smoothing the transition from one engine operation mode to another. At idle, when the throttle is closed, part of the air through the channel of the transition system is mixed with the fuel emulsion. The change in the composition of the mixture is compensated by the selection of jets. When tightening the “quantity” screw, the throttle valve opens slightly. As a result, the air flow through the channel of the transition system decreases, and increases through the gap between the walls of the mixing chamber and the damper. The amount of combustible mixture entering the engine increases, and the speed of the crankshaft increases. When the screw is loosened, the shutter closes and the engine speed decreases.
The main dosing system ensures uninterrupted engine operation only with very smooth opening of the throttle. With a sharp opening of the flap (for example, for intensive acceleration of the car) at the first moment, the process of mixture formation is violated. To eliminate the “failure” in the engine in this mode, the carburetor is equipped with a special device. an accelerator pump. It is designed for short-term enrichment of the combustible mixture with a sharp opening of the throttle. On carburetors, a diaphragm accelerator pump with a drive from the throttle axis is widely used. When the damper is opened, a cam mechanically connected to its axis rotates and presses the diaphragm pusher. When the throttle closes, the cam no longer acts on the plunger. The diaphragm under the action of the return spring moves to its original position, creating a vacuum in the pump cavity. The ball of the discharge valve closes the hole in the well under the sprayer, the ball of the suction valve passes fuel into the pump. Gasoline from the float chamber passes through the suction valve, filling the pump cavity. When you sharply press the “gas” pedal, the cam presses on the telescopic pusher, compressing its spring. In this case, the ball of the discharge valve rises under the fuel pressure, opening the way for fuel from the pump cavity to the atomizer. Abrupt movement of the diaphragm does not occur, because fuel cannot pass quickly through the small nozzle outlet. Since the pusher spring is stiffer than the diaphragm return spring, the first, overcoming the resistance of the latter, moves the diaphragm, displacing a portion of fuel through the discharge valve and atomizer into the carburetor mixing chamber. The injection process is extended in time to several seconds. This ensures stable operation of the engine during acceleration of the car, and, in addition, the diaphragm is protected from rupture under the influence of fuel pressure.
When starting the engine, the crankshaft speed is low, the vacuum in the intake system is small, and gasoline does not evaporate well. In addition, as noted earlier, on a cold engine, especially at low ambient temperatures, most of the generated fuel vapor condenses in the intake tract. Therefore, for a stable engine start, it is necessary to prepare a deliberately re-enriched air-fuel mixture in the carburetor. To do this, close the air damper and open the throttle. Then, a vacuum is created in the diffuser that is sufficient to allow the necessary amount of fuel to flow out of the atomizer, even when the crankshaft rotates slowly. A working mixture suitable for starting the engine is formed. But as soon as the first flashes appear in the cylinders so that the engine does not stall from re-enrichment, it is necessary to open the air damper, opening the way for air to the diffuser. To perform these operations, the carburetor is supplemented with a special starting device. On carburetors of engines of domestic cars, a manually controlled starting device is widely used. It consists of an air damper, an automatic device for opening it slightly and drive elements. The driver closes the air damper from the passenger compartment with the help of a handle, which is connected by a rod to the damper drive. The actuator allows the damper to slightly open, and the return spring tends to keep it in the closed position. A device is installed on the carburetor that automatically opens the air damper by the required amount, which prevents re-enrichment of the combustible mixture immediately after starting. The device consists of a camera with a diaphragm, a spring and traction. The camera channel is connected to the throttle space of the carburetor. With the beginning of stable operation of the engine behind the throttle, a sharp increase in vacuum occurs, from where it is transmitted to the chamber through the channel. The diaphragm, overcoming the resistance of the spring, moves and opens the air damper through the draft, impoverishing the mixture. Due to the fact that the damper is mounted asymmetrically on the axis, under the influence of rarefaction, it tends to open in the mixing chamber, “helping” the starting device. The air damper is connected to the throttle by a mechanism that provides a slight opening of the throttle when the air damper is completely closed. The amount of ajar throttle should ensure the stable operation of the cold engine during heating. As the engine warms up, the driver manually opens the air damper and covers the throttle, reducing the crankshaft speed to a minimum stable.
Power mode economizer
To obtain maximum power from the engine, an enriched fuel mixture is required. For its preparation, the carburetor is equipped with a special system called the power moderator. The system provides additional fuel to the atomizer, bypassing the main fuel jet. To enable the economizer of power modes, a pneumatic or mechanical drive is used. The pneumatic actuator is triggered when the vacuum drops in the mixing chamber, and not as the throttle opens. This makes it possible to enrich the mixture to the right extent during acceleration of the car, providing good throttle response, and to maintain a lean mixture with uniform movement, providing efficiency. With the throttle closed, the vacuum from the throttle space enters the diaphragm of the economizer through the channel. In this case, the diaphragm compresses the return spring, and its pusher does not touch the economizer valve ball, and the valve is closed. When you open the throttle, the vacuum under it (respectively, at the diaphragm) decreases. Under the action of the spring, the diaphragm shifts, and its pusher, recessing the ball of the valve, opens the channel of the economizer. Additional fuel from the float chamber enters the atomizer of the main metering system, enriching the mixture.
Econostat is intended for additional enrichment of the combustible mixture at maximum load conditions at a high rotational speed of the crankshaft. Econostat is a spray mounted in the very top of the mixing chamber, above the diffuser. Fuel is supplied to it directly from the float chamber through a channel in which a fuel nozzle is installed, which prevents re-enrichment of the combustible mixture. Sometimes, for finer tuning of the economizer, an air nozzle is additionally installed in the upper part of the channel. Air is introduced through it, which is mixed in the channel with fuel. Since the spray outlet is located in the low vacuum zone, the economizer only starts up when the throttle is fully open. At the same time, the crankshaft rotation speed should be high enough so that a vacuum is generated in the area of the outlet of the sprayer sufficient to raise the fuel in the channel to the level of the sprayer. The fuel supplied through the atomizer is mixed with the flow of the fuel-air mixture, further enriching it.
Dual chamber carburetor
To improve the mixture formation and distribution of the combustible mixture over the cylinders, it is necessary to provide low resistance to air movement through the carburetor diffuser at high loads and to maintain sufficient vacuum in it at low loads. These requirements are most satisfied by the design of a two-chamber carburetor with sequential inclusion of cameras. The first chamber. the main one. provides engine operation at idle, as well as at small and medium loads. The second. additional. is included in the work at high loads. The throttle actuator of the second chamber may be mechanical or pneumatic. In the first case, the opening of the second chamber damper starts at a certain opening angle of the throttle valve of the first chamber. In the second case, the opening moment depends on the amount of vacuum in the mixing chambers.