Chainsaw is one of the irreplaceabletools in a private household. It is very important that this tool functions continuously and without interruption. The quality of the chainsaw's operation largely depends on the reliability of the carburetor. As it is used Walbro. This carburetor is quite reliable. But he sometimes needs adjustment, prevention and repair. Well, let's look at the features of this node.

Mechanism arrangement

The device is supplied in an aluminum casing,which is made by casting. Inside it there are internal channels with contours. These are diffusers. Air passes through them, which is then sucked up by the internal combustion engine.

walbro carburetor
The diffuser has fuel channels. When air passes through the element, it is connected to the gasoline stream, forming a combustible mixture. The fuel pump, the system of jets, as well as the mechanism that allows you to adjust the parameters of the mixture, are installed from the outside and are integrated into the Walbro carburetor. The power that can be developed by the engine chainsaw, as well as the amount of air in the carburetor, is regulated by the throttle. Pump impulse chamber for fuel injection. It is delivered via a pulse channel, which 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 membrane. The pump is forced to start, while its operation is synchronized with changes in pressure in the crankcase. Its level depends on the engine speed. The fuel is fed to the carburetor from the tank through a special carburettor fitting. Passes through a diaphragm, an inlet and an exhaust valve on the fuel pump, and also through the filter. Then the mixture along the fuel channel past the needle enters the chamber where the control membrane is located. Needle valve, or rather a needle, with the aid of a lever is in connection with the membrane. The chamber below it, through a special hole, opens into the atmosphere.

Operating principle

Carburetor Walbro for chainsaw functions forthe pressure change in the crankcase of the motor. At the beginning of the intake stroke, the air begins to flow through the diffuser by means of a vacuum. Its volume depends on the speed of the motor and its load.

carburetor walbro
Also, it depends on what positionis the throttle. It is controlled by a special handle. Using fuel jets, during the passage of air, a mixture is formed. Next, gasoline is sprayed and a finished mixture is obtained, optimal for combustion. Usually, it is prepared in a proportion of 1 to 14. Then the mixture will fall into the cylinders, where the combustion cycle takes place. Due to the fact that the volume below the control membrane is connected to the atmosphere, it is shifted upwards. Then, using the lever, it pulls the needle behind it, opening the fuel channel. So, the next dose of fuel gets into the camera. As the fuel chamber is filled with gasoline, the membrane will go to its usual place. The needle valve closes and, as a result, the right amount of gasoline appears inside the chamber. It will be fed through jets. This process is cyclical and constantly repeated. To adjust the amount of fuel that will come from fuel jets, there is a diffuser. The Walbro carburetor is equipped with adjusting screws. The first - the main, the second - to adjust the idle. As a result of the rotation of these screws, the mixture is enriched or impoverished. If you twist them, then the mixture becomes richer. If you twist - will become poor.
carburetor walbro for chainsaws
It is necessary to choose the optimal ratio to1 kg of fuel accounted for 14 kilograms of air. The manufacturer has additionally provided the possibility of adjusting the idling speed. This screw can be found from the outside. If you twist it, it rests against the lever installed on the throttle shaft. By rotating these screws, you can independently adjust the carburetor to obtain the required power in a variety of conditions.

How to understand that the carburettor adjustment is required?

There are several features that canTalk about the incorrect operation of the Walbro device. Carburetor in these cases must be adjusted. If the engine chainsaw starts with great difficulty and immediately after the start of stall, the cause of this phenomenon in a non-optimal fuel mixture. In other words, she is too poor. Also, the carburetor requires tuning, if suddenly the saw began consuming too much fuel. Another of the signs is the more amount of exhaust gas. This is a signal that the mixture burns incompletely. She's too rich. The fixing screws may be broken. This happens due to strong vibrations and various defects of the protective cap. This phenomenon is very rare in Walbro products. The carburetor can then be easily repaired. Another problem is clogging. Often, the carburetor channels, diffuser and cavities may become dirty due to poor quality fuel or a defective air filter. Too worn out engine pistons also affect the operation of the carburetor.

carburetor repair walbro
In this case, the adjustment of the carburetor Walbro, if it helps to solve the problem, it is only temporary. In this situation, it is necessary to perform a major overhaul of the motor.

Identification of problems in the carburetor and typical faults

Often owners of chainsaws face a leakfuel. To diagnose this, an external inspection is necessary. To do this, the device is recommended to remove and check the integrity of the gasket. It can be found between the device and the engine casing. If the gasket is in order, then check the device for leaks. All faults, which we will consider below, affect the level of tightness. Many of them can be corrected if you purchase a repair kit for the Walbro carburetor and replace the damaged or broken parts.

How to check the tightness?

The fuel supply hose is put on the inlet channelmeasuring device. Then the faucet opens, if there is one. Further, a certain amount of air is pumped into the cavity of the carburetor. In this case, the manometer should show at least 0.4 bar. If after a while the pressure remains the same, then you have a working carburettor Walbro. Repair is necessary if the pressure drops. There may be several reasons.

carburetor walbro adjustment
This is a malfunction of the fuel pump membrane. It may be damaged. There are holes or tears on it. The fault is rectified by replacing the diaphragm with a new one from the repair kit.

Needle valve

Sometimes the needle in the valve can not fullyclose it. This situation can occur due to blockages, heavy wear or a damaged needle cone. The lever of the valve also loses its mobility, its geometry is disturbed. The elasticity of the spring changes.


The tightness is reduced due to the loss of the shape of the control membrane. This can occur due to overheating, prolonged operation of the device.

Inlet and outlet valve

This problem can occur in the fuel pump.

carburetor walbro repair
The fact is that the petals of the valves leave them"Flatness". They no longer cling to their supporting planes, the tightness is broken. As a result - loss of productivity of the pump. He no longer pumps fuel in the right amount. Why does this happen? Everything is very simple. The owner has long used a saw with a different fuel, and not the one recommended by the manufacturer Walbro. The carburetor is often overheated because of this. As a result of such a malfunction, a too poor mixture is prepared, the engine is poorly lubricated. This can lead to more serious problems. This is a teaser in the cylinders, problems with start-up, unstable operation of the unit in all modes. Also among the problems with the fuel pump can be identified deformation of the membrane in the impulse chamber area, pollution and slags. Many symptoms in the carburetor's work are often associated with clogging. Cleaning and rinsing can restore the operation of the device. To do this, there is a special spray.

Adjusting the carburetor

The setup process is pretty simple, especially ifalready have a similar experience. The first thing you need to do is to tighten the screws, which are responsible for the maximum and minimum revolutions, in a clockwise direction. They can be designated as H and L. They should be screwed to the stop. Then, for half the turn, the screws are unscrewed. All manipulations are carried out on a muffled motor. After completing this procedure, the motor must be started and warmed up at medium revs.

Idling adjustment

This screw is recommended to be screwed in a counter-clockwise direction until the engine runs as smoothly as possible.

carburettor tuning walbro
It is important to see if the chain is moving. If it rotates, then it is necessary to tighten the screw. When the engine starts to stall in this mode, the screw is slightly unscrewed back.

Testing work after setup

It is necessary to check how the carburettor worksWalbro. Adjustment may not produce the desired result. For testing, the engine is started, heated and gently pressed on the accelerator. If, as a result, the turnover has risen to the maximum, then everything works correctly. If this does not happen, screw L is turned anti-clockwise by 1/8 turn. The maximum engine speed of the chainsaw is about 11.5 thousand revolutions per minute. If their number is higher, this can cause disturbances in the ignition system. In the event of a malfunction, screw H is turned counter-clockwise, thereby reducing the maximum speed.


Knowing the Walbro carburetor device and its principleaction, you can easily adjust it to work in the required modes. The device is simple and can cope with it even people without experience. Any problems can be eliminated with their own hands without significant costs.