A chainsaw is one of the indispensable tools in a private household. It is very important that this tool functions constantly and without interruption. The quality of the chainsaw largely depends on the reliability of the carburetor. Walbro is used as it. This carburetor is quite reliable. But he sometimes needs adjustment, prevention and repair. Well, let's look at the features of this node.
Mechanism device
The device comes in a die-cast aluminum case. Inside it there are internal channels with contours. These are diffusers. Air passes through them, which is then sucked in by the internal combustion engine.
The diffuser has fuel channels. When air passes through the element, it flows with gasoline, forming a combustible mixture. Fuel pump, jet system, as well as a mechanism that allowsadjust the mixture settings, are installed externally and built into the Walbro carburetor. The power that the chainsaw engine can develop, as well as the amount of air in the carburetor, is controlled by the throttle. Impulse chamber of the pump for pumping fuel. It is supplied through an impulse channel that connects to the motor boat. When the piston in the cylinder moves, the pressure in the crankcase changes. These changes affect the operation of the fuel pump diaphragm. The pump is forced to start, while its operation is synchronized with changes in crankcase pressure. Its level depends on the engine speed. Fuel is supplied to the carburetor from the tank through a special carburetor fitting. Passes through the diaphragm, inlet and outlet valves on the fuel pump, and through the filter. Further, the mixture through the fuel channel past the needle enters the chamber where the control membrane is located. The needle valve, or rather the needle, is connected to the membrane by means of a lever. The chamber below it exits through a special hole into the atmosphere.
Operation principle
Walbro chainsaw carburetor functions by changing the pressures in the crankcase. At the beginning of the suction stroke, air begins to pass through the diffuser through vacuum. Its volume depends on the engine speed and its load.
It also depends on what position the throttle is in. It is controlled by a special handle. With the help of fuel jets, during the passage of air, a mixture is formed. Next gasolinesprayed and a ready mixture is obtained, optimal for combustion. Usually it is prepared in a ratio of 1 to 14. Next, the mixture enters the cylinders, where the combustion stroke occurs. Due to the fact that the volume below the control membrane is connected to the atmosphere, it shifts upward. Further, with the help of a lever, she pulls the needle behind her, while opening the fuel channel. So, another dose of fuel enters the chamber. As the fuel chamber fills with gasoline, the membrane will go to its usual place. The needle valve will close and as a result, the right amount of gasoline will appear inside the chamber. It will be fed through jets. This process is cyclical and constantly repeats. To adjust the amount of fuel that will come from the fuel jets, there is a diffuser. The Walbro carburetor is equipped with tuning screws. The first is the main one, the second is for adjusting the idle speed. As a result of the rotation of these screws, the mixture is enriched or depleted. If you twist them, then the mixture becomes richer. If you twist it, it will get poorer.
It is necessary to choose the optimal ratio so that 14 kilograms of air fall on 1 kg of fuel. The manufacturer additionally provided for the possibility of adjusting the idle speed. This screw can be found outside. If you screw it in, it will rest against the lever mounted on the throttle axis. By turning these screws, you can independently tune the carburetor to obtain the necessary power in a variety of conditions.
How to understand that adjustment is requiredcarburetor?
There are several signs that may indicate incorrect operation of the Walbro appliance. The carburetor in these cases must be adjusted. If the chainsaw engine starts with great difficulty and stalls immediately after starting, the cause of this phenomenon is a suboptimal fuel mixture. In other words, she is unnecessarily poor. Also, the carburetor requires adjustment if the saw suddenly began to consume too much fuel. Another sign is more exhaust gases. This is a signal that the mixture does not burn completely. She is too rich. Adjustment screws may be loose. This happens due to strong vibrations and various defects in the protective cap. This phenomenon is very rare in Walbro products. The carburetor can then be easily repaired. Another problem is congestion. Often the carburetor channels, diffuser and cavities can become dirty due to poor-quality fuel or a faulty air filter. Excessively worn engine pistons also affect the performance of the carburetor.
In this case, adjusting the Walbro carburetor, if it helps to solve the problem, then only temporarily. In this situation, it is necessary to overhaul the motor.
Identification of problems in the operation of the carburetor and typical malfunctions
Often chainsaw owners are faced with a fuel leak. To diagnose this, it is necessary to make an external examination. To do this, it is recommended to remove the device and check the integrity of the gasket. It can be found between the device and the crankcase. If everything is in order with the gasket, then the device is checked for leaks. All malfunctions, which we will consider next, affect the level of tightness. Many of these can be fixed by purchasing a Walbro carburetor repair kit and replacing damaged or failed parts.
How to check the tightness?
The fuel supply hose is put on the inlet channel of the measuring device. Then the faucet opens, if there is one. Next, a certain amount of air is pumped into the cavity of the carburetor with a pear. In this case, the pressure gauge should show at least 0.4 bar. If the pressure stays the same after a while, then you have a good Walbro carburetor. Repair is needed if the pressure drops. There may be several reasons for this.
This is a fuel pump diaphragm failure. It may be damaged. It has holes or breaks. The malfunction is eliminated by replacing the membrane with a new one, from the repair kit.
Needle valve
Sometimes the needle in the valve cannot completely close it. This situation may occur due to blockages, heavy wear or a damaged needle cone. The valve lever also loses its mobility, its geometry is disturbed. The elasticity of the spring changes.
Membrane
Tightness is reduced due to loss of shape of the control diaphragm. This may occur due to overheating, prolonged operation of the device.
Inlet and outlet valve
This problem may be in the fuel pump.
The fact is that the valve petals lose their “flatness”. They are no longer pressed against their supporting planes, the tightness is broken. The result is a loss of pump performance. It no longer pumps fuel in the right amount. Why does this happen? Everything is very simple. The owner has been using the saw for a long time with a fuel other than the one recommended by the Walbro manufacturer. Because of this, the carburetor often overheated. As a result of such a malfunction, a too lean mixture is prepared, the engine is poorly lubricated. This can lead to more serious problems. These are seizures in the cylinders, starting problems, unstable operation of the unit in all modes. Also, among the problems with the fuel pump, deformations of the membrane in the area of \u200b\u200bthe impulse chamber, pollution and slag can be distinguished. Many carburetor symptoms are often associated with blockages. Cleaning and rinsing can restore device performance. There is a special spray for this.
Carburetor adjustment
The setup process is quite simple, especially if you already have a similar experience. The first thing to do is to tighten the screws that are responsible for the maximum and minimum revolutions clockwise. They can be designated as H and L. They should be screwed in until they stop. Then unscrew the screws half a turn. All manipulations are performed on a muffled motor. After completing this procedure, the engine must be started and warmed up at medium speed.
Idling setting
It is recommended to turn this screw counterclockwise untilthe engine will run as smoothly as possible.
It is important to keep track of whether the chain is moving. If it rotates, then you should still tighten the screw. When the motor starts to stall in this mode, the screw is slightly unscrewed back.
Testing work after setup
Must check how the Walbro carb works. Adjustment may not give the desired result. For testing, the engine is started, warmed up and smoothly pressed on the accelerator. If as a result the speed has increased to a maximum, then everything is working correctly. If this does not happen, screw L is turned counterclockwise by 1/8 turn. The maximum engine speed of the chainsaw is approximately 11.5 thousand revolutions per minute. If their number is higher, this can cause malfunctions in the ignition system. In case of malfunctions, screw H is turned counterclockwise, thereby reducing the maximum speed.
Conclusion
Knowing the structure of the Walbro carburetor and the principle of its operation, you can easily adjust it to work in the required modes. The device is simple and even people with no experience can cope with it. Any problems can be fixed by hand at no significant cost.
