How to adjust the carburetor of chainsaw correctly
Let's start with the needle. Is this needle LD? Bolts (that is, pins with conical surfaces) are used to adjust the idle speed. Increase the idle speed clockwise and lower the idle speed counterclockwise. LD？ Usually, the bolt can be adjusted to change the idle speed. Keep the idle speed at 2500-2800 rpm.
If there are three needles on the carburetor. Is it h, l and LA? Three kinds of bolts. H bolt is a high-speed adjusting bolt, and the fuel supply can be adjusted by adjusting the nozzle inside the carburetor to adjust the high speed. Generally speaking, it is not easy to adjust the H bolt. The initial position of H bolt is counterclockwise to the end, at which time the oil supply is the maximum. L bolts are idle bolts. Adjust the fuel supply and idle speed by adjusting the nozzle inside the carburetor. Generally speaking, it is not easy to adjust the L bolt. Due to different machine manufacturers and models, some idling bolts may be locked and some are not, so the initial position is analyzed in detail. Generally, it is also adjusted counterclockwise. Los Angeles? Bolt has the same function as LD? Like bolts. Adjust the idle speed by adjusting the throttle.
The carburetor with simple expansion data consists of three parts: the upper part has an air inlet and a float chamber, the middle part has a throat, a measuring hole and a nozzle, and the lower part has a throttle valve. The float chamber is a rectangular container for storing gasoline from a gasoline pump. There is a float in the container, and the oil intake is controlled by the height (oil level) of the floating surface. The oil inlet at one end of the middle nozzle is communicated with the metering hole in the float chamber, and the oil outlet at the other end is located at the throat of the throat.
The throat is shaped like the waist of a bee, with two big ends and a small middle, and the cross-sectional area of the middle throat is the smallest. When the engine is started, the piston descends to generate suction, and the inhaled airflow passes through the throat at the highest speed, but the static pressure is the lowest, so the throat pressure is lower than atmospheric pressure, that is to say, there is a pressure difference between the throat and the float chamber, which is often called "vacuum degree". The greater the pressure difference, the greater the vacuum degree. Gasoline is ejected from the oil outlet of the nozzle under the action of vacuum. Because the airflow speed at the throat is 25 times that of gasoline, the oil flow ejected from the nozzle is dispersed by the high-speed airflow, forming atomized particles with different sizes, that is, "atomization". The preliminarily atomized engine oil particles are mixed with air to form a "mixed gas", which enters the combustion chamber of the cylinder through the throttle valve, the intake pipe (4) and the intake valve (5). Here, the throttle opening and engine speed determine the vacuum degree of the throat, and the throttle opening directly affects the proportion of the mixture, which is an important reason for affecting the engine operation.
This involves the concept of "air-fuel ratio". The so-called air-fuel ratio refers to the ratio of air quality to fuel quality. Scientists believe that 1 kg gasoline needs about 14.7 kg air to burn completely, that is, the air-fuel ratio is 14.7: 1. This air-fuel ratio mixture is called standard mixture, and it is also called "theoretical mixture" because it is difficult to reach this value in practice. The mixture with air-fuel ratio greater than the standard is called lean mixture, and the mixture with air-fuel ratio less than the standard is called rich mixture.
Because the concentration change of mixed gas is closely related to the load change of the engine under various working conditions, the simple carburetor can not meet the requirements of changing at any time, so people continue to add new devices to the simple carburetor to adjust the working state of the carburetor. Up to now, carburetors with various auxiliary devices have been formed, mainly including idling, enrichment, acceleration and starting devices. At present, the common carburetor of 4-cylinder engine is a double-cavity transfer carburetor, which has two throats and works separately or simultaneously according to different engine working conditions. The common carburetor of a six-cylinder engine is a dual-chamber parallel carburetor. In fact, two single-chamber carburetors are connected together, and each chamber is responsible for supplying air to half of the cylinders. There are also multi-cavity carburetors, which are generally assembled on high-power engines.
In the multi-functional device of carburetor, the main oil supply device is the basic oil supply structure of carburetor, which is needed by various working conditions of engine except idle speed. Idling device is a device that provides a small but rich mixture at idle speed to maintain the stable minimum speed of the engine. The enrichment device is an additional fuel supply device when the engine is under heavy load to make up for the shortage of main fuel supply. Throttle is a device that provides extra fuel when the throttle opening suddenly increases when the car accelerates, which makes the engine speed and power increase rapidly. The starting device is a device that provides extremely rich mixture when the engine is cold started. The common method is to install a choke valve in front of the throat to control the air intake.
Idle speed should be mentioned here in particular. Idle speed is the most commonly used engine working condition, which is used for engine warm-up process and non-flameout shutdown. It is of great significance to the driving performance of automobiles, especially when driving in cities. Idle speed often determines the fuel consumption and pollution discharge of a car.
Generally, the idle speed of the engine is only 600-800 rpm, and the throttle valve is close to closing. The throat vacuum generated by this speed cannot smoothly suck gasoline out of the float chamber, but the vacuum behind the throttle valve is very high. Therefore, it is only necessary to set an idle oil circuit on the basis of a simple carburetor, and its spray hole is set behind the throttle valve, and the problem is solved.
Because the mixture required for idling is small and thick, it is sensitive to the running condition of the engine. In order to realize the idle state with stability and minimum speed, it is necessary to adjust the fuel quantity control and the minimum throttle opening. The existing carburetor idling device has two adjusting screws to adjust the fuel quantity and throttle opening respectively. At the same time, in order to prevent the car from turning off the ignition switch when the engine is still running, an idle solenoid valve is installed in the idle oil circuit of the carburetor, which is responsible for opening and closing the idle oil circuit to ensure that the engine can be quickly turned off.
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