Adjusting the walbro carburetor on a brushcutter

Adjusting a chainsaw carburetor

chainsaws are very popular gardening tools. They have become very popular with gardeners and those who care for the area in their yards. Building or repairing work cannot be done without chainsaws. Chainsaws are even more important in the logging profession.

Every chainsaw requires proper care, maintenance and adjustment before use. Stressing too much can shorten the tool’s service life and damage it.

Today we will talk about the part of the chainsaw mechanism, whose task is to prepare fuel before it is fed into the engine cylinder. This is the function of your chainsaw carburetor. It is what will determine how well the chainsaw works and how much fuel it uses when it is running. If you see that your chain saw is not running smoothly, you may need to adjust the carburetor.

When the chainsaw carburetor needs adjustment?

Here is a list of the most common cases in which a chainsaw carburetor tune-up is needed:

  • The engine starts but the chain saw stops or fails to start. The reason may be that there is too much air in the fuel tank.
  • Increased fuel consumption. It can occur due to excessive saturation of the mixture that enters the engine with fuel. In order for the engine to run well, the mixture must be of good quality.
  • The bolts in the carburetor have lost their hold due to a damaged carburetor housing.
  • Debris in carburetor. This can happen if the filter is damaged or low-quality fuel is used. You will need to completely disassemble the carburetor, rinse it and readjust it.
  • The engine does not run well at idle or does not develop full power.

Important! If the engine runs poorly because the piston is worn, adjusting the carburetor will not work. In addition, along with the adjustment it is advisable to clean the carburetor of debris. this will increase the effectiveness of the procedure.

Walbro carburetor for chainsaw 4500-5200 (0456)

Walbro carburetor for chain saw. The purpose of the carburetor is primarily to correctly proportion fuel and air and convert them into a fuel mixture. On a Walbro carburetor there are regulating jets that regulate idle speed and fuel supply. Also a chainsaw carburetor has an air and throttle valve. The carburetor is suitable for all Chinese chainsaws. Walbro carburetor is a carburetor of the well-known brand of spare parts, which is popular all over the world.

How to replace the Walbro carburetor on a 4500-5200 chainsaw.

You can replace the carburetor on your chainsaw yourself without using special tools.

  • Remove the filter cover
  • Remove the air filter
  • disconnect the choke and choke lever
  • Disconnect the fuel hoses from the carburetor
  • under the air filter elbow are two mounting bolts that need to be unscrewed
  • After removing the carburetor from its seat
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To install the carburetor on your chainsaw, do all these steps in reverse order.

How to adjust the carburetor Walbro on your chain saw. Adjusting the carburetor is a very difficult process, best left to an expert. Since after adjustment you will break the factory settings of the chainsaw.

Buy a carburetor for a chain saw you can in our online store through the cart or contact our manager and he will help you with the choice of products. Delivery in any city of Ukraine: Kiev, Lviv, Odessa, Dnepropetrovsk, Kharkiv, etc.

Working principle

The carburetor is the module of the power system in which liquid fuel and air are mixed before being fed into the engine cylinders. Depending on the tool and its mode of operation, mixing and feeding are adjusted accordingly.

The design of the lawnmower carburetor is the same in almost all cases. Refers to the category of float-operated devices. The latter ensure stable parameters of prepared mixtures.

  • The air enters the body of the tube with the air damper. The latter increases or decreases the air flow depending on its position.
  • In the area where the orifice for gasoline supply is formed, the tube has a narrowing. a diffuser. Here the flow rate increases.
  • Fuel flows from the float chamber to the tube through the nozzle. The float level determines the volume of fed fuel. Since the pressure in the chamber is normal and the tube is low because of the greater rarefaction of air, the gasoline is sucked through the nozzle.
  • Accelerated air flow picks up fuel and atomizes it, forming an air-fuel mixture of the desired density.
  • The mixture is sucked into the cylinder through a pipe.

The more open the air damper in the tube, the higher the density of air flow, and therefore more fuel enters the cylinder. Tuning the lawnmower carburetor comes down to setting the ratio of the flaps in such a way that the density of the fuel mixture becomes optimal.

When to adjust the carburetor in a trimmer?

It is necessary to adjust the device in such cases:

adjusting, walbro, carburetor, brushcutter
  • The new engine used 5 liters of fuel in one go.
  • The weather has changed (sudden change in atmospheric pressure).
  • You bought a different brand of oil or gasoline.
  • During long storage periods.
  • Screws unscrewed by themselves after vibration.
  • The consumption of gasoline has increased, the carburetor began to overflow.
  • Carbon deposits on internal spark plug electrodes.
  • No gasoline in the cylinders.
  • The engine frequently stalls or does not pick up enough rpm.

When to adjust the carburetor in a trimmer?

It is necessary to adjust the device in such cases:

  • New engine used 5L of fuel in one go.
  • The weather changes (sudden drop in atmospheric pressure).
  • You have bought a different brand of oil or gasoline.
  • During prolonged storage.
  • After vibration, the screws unscrewed on their own.
  • Gasoline consumption has increased, the carburetor began to overflow fuel.
  • There is soot on the inside electrodes of the spark plug.
  • No more gasoline is getting into the cylinders.
  • The motor frequently stalls or does not pick up enough speed.
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Adjusting the brushcutter carburetor

Before adjusting, you need to clean the filters very carefully. This should be done according to the manufacturer’s instructions. Further work with the carburetor is made by adjusting the three screws.

  • Right screw. air-fuel mixture adjustment. Left and right rotation of the screw is performed at idle speed. The maximum rpm should be determined.
  • Left screw. air-fuel mixture adjustment. The work is performed at high rpm. Screw is the last to be adjusted; correct adjustment will influence engine power and gasoline consumption.
  • Bottom screw. motor control. Work is performed at idle speed. Turning clockwise indicates increasing, counterclockwise indicates decreasing.

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EnerSol EPG-2800S gasoline generator

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How to adjust the carburetor of a chainsaw. tips and tricks

The carburetor has three adjustment screws:

Use the H and L screws to adjust the fuel/air mixture ratio determined by the throttle opening. When tightening the screws (clockwise) the mixture is depleted. low revolutions, when unscrewing the screws (counterclockwise) the mixture is enriched, the revolutions increase.The T screw regulates the idle speed. Turning clockwise increases RPM, counterclockwise decreases RPM.Basic adjustment of the carburetor is done at the factory when the saw is tested. The carburettor is set for a richer-than-optimum mixture. This regulation is to be maintained during the first hours of operation. Then fine-tune the carburetor.

When rotating the chain at idle you need to turn the T screw counterclockwise until the chain stops.Precise carburetor adjustment can be performed only in warmed up condition by specialists with special equipment (rev counter).First adjust the L screw, then the H screw, and finally the T screw. First find the highest idle speed by slowly turning the L screw clockwise (or counterclockwise). After having found the highest revolution position turn the L screw a quarter of a turn anticlockwise. If the chain still rotates at idle speed, turn the T screw clockwise until the chain stops.Adjustment of screw H affects power and rpm. Adjusting the carburetor to a lean mixture will result in excessive RPM and damage to the saw.After engine is warmed up at full throttle for 10 seconds turn the screw H about 1/4 turn counterclockwise. Let the engine run for about 10 seconds. Check the maximum rpm with the tachometer. Repeat the operation in case of discrepancy between the maximum rpm and the passport rpm. The engine should sound like a four-stroke. If the mixture is too loose, the saw squeals. If the mixture is too rich, the carburettor starts to smoke.For optimum adjustment have a specialist have access to a tachometer.After adjusting the L and H screws, fine adjust the idle speed with the T screw.if the idle speed has to be adjusted, with the engine running turn the screw T clockwise until the saw chain starts to rotate. Then turn the screw back counterclockwise until the chain stops turning. The idle speed is set correctly if the engine is running evenly in all positions and there is sufficient idle speed margin when the chain starts to rotate.The carburettor is set correctly if the engine accelerates immediately and makes a noise like a four-stroke at full throttle. Adjusting the L screw to a too lean mixture leads to difficult starting and poor acceleration of the engine. Based on materials from the site Ie5107

WALBRO carburetors and their features

In starting this article, I do not claim to be “the final authority”. therefore, any criticism, pointing out errors in the semantic content of the article and even in grammar are accepted in any form and to any extent. I would be glad to get some feedback. This article doesn’t describe any particular carburetor model, since it is impossible to cover the whole range of carburetors produced by Walbro in this article. But taking into account the increasing spread of large-cube engines in modeling (which are equipped with a carburetor Walbro), I would like to explain the principle of operation and physical processes occurring in carburetors with a built-in fuel pump. Understanding and correct understanding of the processes occurring in the carburetor will enable the user to operate correctly and quickly eliminate any deviations from normal operation.

The carburetor’s job is to mix the fuel and air in the optimum ratio for all engine operating conditions, and by atomizing the fuel prepare the mixture for evaporation. the fuel is atomized in the carburettor and only a small part of it evaporates. (certain efforts are made by the manufacturer for this. for example, a thermally insulating gasket between the carburetor and the engine crankcase). Heat necessary for fuel evaporation, is taken from the parts of the power plant itself, with which the fuel mixture is in contact during its flow in the intake channel. And a further complete evaporation of the fuel mixture already takes place in the engine cylinder.

The extraction of heat from engine parts, necessary for the evaporation of the fuel mixture, causing cooling of these parts is called internal cooling.

Theoretically with a fuel mixture of 14.8 kg of air and 1.0 kg of gasoline the air lambda number = 1 At this ratio the fuel mixture burns completely. This ratio is called the ideal ratio. Fuel mixture is combustible at lambda values between 0.7 and 1.25.

real properties of fuel mixtures differ from theoretical ones depending on external conditions (temperature, air humidity, atmospheric pressure) and on the modes of engine operation (starting, idling, part load, full load). If the real mixture composition differs from the ideal one, then the mixture is either poor or rich.

Poor mixture contains more air When the mixture is lean, the engine does not develop full power because of the lack of fuel in the mixture, besides the engine has an increased temperature because of poor internal cooling. Because of the reduced volume of oil-containing new portion of the fuel mixture, the lubrication conditions worsen, which leads to an increased risk of scuffing the piston-cylinder pair.

A rich mixture contains less air. If the mixture is rich, the fuel mixture is incompletely combusted. Unburned mixture shows itself also in the form of smoke from the muffler.

Design and Function Let’s look at the general structure of a carburetor with an integrated fuel pump. Carburetor

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Reference. Read to Know What You’re Doing!

The desired composition (quality) of the fuel/air mixture is adjusted (changed) by turning the fuel adjustment screws in the intake air flow (right and left). The amount of mixture entering the cylinder is metered by the throttle valve. If you turn them clockwise the mixture sucked into the cylinder becomes leaner (less fuel in the air/fuel ratio) and the engine rpm increases, the Husqvarna engine runs softer (has lower rpm) and the output drops dramatically. Besides, with higher revolutions, less oil (worse lubrication) gets into the cylinder with the lean mixture and so you can screw up the engine. And the grass trimmer won’t start well. If the screws are turned counterclockwise, the mixture sucked into the cylinder is enriched (more fuel in the air/fuel ratio) and the engine speed decreases, while at lower rpm more gasoline and oil gets into the cylinder (better traction, better lubrication), but the Husqvarna engine “untwists” badly (does not gain speed) and more sludge is formed in the cylinder!

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Arboretum carburetor unit

The standard design of any gas grass trimmer should include a fuel system based on the action of a standard carburetor. Its structure and initial principle of operation is almost the same for all mowers, regardless of their design features and purpose.

The braid carburetor consists of an all-metal aluminum housing that protects the internal components from moisture, fine dirt and dust. The lower part of the body is equipped with an integrated diffuser, the second name of which is. “Venturi nozzle”. The main function of this standard part is to supply air in the quantity needed by the fuel block to enrich the fuel. The diffuser works on a simple principle: the smaller its diameter, the more air is sucked in. This is because in the area with the smallest diameter, the air supply is at its maximum.

The upper part of the built-in factory diffuser is pre-equipped with fuel tubes, through which the fuel mixture is drawn in under the influence of air. Other parts of the carburetor: The regular adjusting screws and fuel pump can be located either inside or outside the carburetor.

The hedge trimmer carburetor includes a throttle whose main task is. Regulating the volume of intake air. The higher the amount of air, the higher the power rating of the grass trimmer power unit. Another function of the damper is to facilitate the cold start of the engine. When the brush cutter is started for the first time after a long period of inactivity the choke must be closed. Immediately after starting the engine, the part must be open, otherwise the engine will shut down.

The carburettor grass trimmer is equipped with a pulse channel that connects the inner cavity of the crankcase to the pulse chamber of the pump. The piston located in the engine cylinder creates a reciprocating motion that causes a gradual change in pressure inside the crankcase. The diaphragm is retained at the same time. The pump action is therefore completely synchronized with the power unit.

The diaphragm of a conventional carburetor takes an active part in the suction of fuel. It enters the fuel assembly through a fitting. The fuel then passes through the built-in intake and exhaust valves, then through a strainer and fuel line. Fuel then flows near the needle and gradually fills the chamber provided with a control diaphragm.

The conventional trimmer carburetor valve is connected to the diaphragm by a lever. At the bottom of the built-in diaphragm, there is a cavity in which air is introduced through a special hole.

The carburetor for gasoline-powered braids works according to this principle in stages. This enables the fuel unit to work smoothly and deliver fuel smoothly into the cylinder of a standard power unit.

Proper adjustment

Chain saw and chainsaw carburetor adjustments are critical for chain saws and other two-stroke engines. Adjustments that give too rich a mixture will cause the saw to have insufficient power, increase carbon and can damage the engine. Proper carburetor tuning will maximize equipment power, prolong engine cycles, produce minimal exhaust, and run smoothly and uninterrupted. Most chainsaws have three carburetor mounting screws:

  • Throttle stop is the adjustment that determines how much the throttle valve stays open when the throttle trigger is released. If this setting is set low, the engine will stall when the throttle trigger is released.
  • Low Speed Fuel Adjustment (L). Adjustment that controls fuel at idle speed.
  • High-speed fuel adjustment (H). controls the proportion of fuel at rated operating speed. This is the most important setting.

It should be noted that some chainsaw designs do not have a high-speed adjustment needle. These saws have what is called a stationary jet, which is set by the factory. Fixed-jet carburetors are used to prohibit the operator from making adjustments himself, which can damage the saw. Unfortunately, these factory settings often do not allow the saw to reach its maximum performance.

How a chainsaw carburetor works. the purpose of the regulators

Returning to our scheme, it is worth mentioning why we need adjustment screws.

The diagram shows that the screw on the right side of 10 is designed to set the idle speed and average speed. Screw 17 on the left side adjusts the fuel flow at high rpm. The details of carburetor adjustment are described in another article on this site.

Guided by the instructions for adjusting the carburetor of a chainsaw, it is not very difficult to make the appropriate manipulations correctly. If you want to tune your chainsaw as accurately as possible, you need a special tachometer. You can buy a tachometer for a chainsaw at a tool store or online, especially since its price is not as high as it costs to repair a chainsaw carburetor.

Detailed step-by-step description of how the chainsaw carburetor works, is described in detail in the video material.

Tuning a walbro carburetor

By starting this article, I don’t claim to be the “final authority”. therefore, any criticism, pointing out errors in the semantic content of the article and even in grammar are accepted in any form and to any extent. I would be glad to get feedback and suggestions. In the article we did not consider a particular carburetor model, as it is simply impossible to cover the entire range of carburetors, manufactured by Walbro, in the article. But considering the increasing spread of large-cube engines in modeling (which are also equipped with a carburetor Walbro), I would like to explain the principle of operation and physical processes occurring in carburetors with a built-in fuel pump. Understanding and proper understanding of the processes that occur in the carburetor will allow the user to operate correctly and quickly correct any deviations from normal operation.

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The carburetor’s tasks include mixing fuel and air in the optimum ratio for any engine operating conditions, and, as a result of atomizing the fuel, preparing the mixture for evaporation. Fuel is atomized in the carburetor and only a small part of it evaporates. (certain efforts are made by the manufacturer for this. for example, a thermally insulating gasket between the carburetor and the engine crankcase). Heat necessary for fuel evaporation is taken from the power plant parts that the fuel mixture comes into contact with during its flow in the intake manifold. And further complete evaporation of the fuel mixture occurs already in the engine cylinder.

extraction of heat from the engine parts, necessary for the evaporation of the fuel mixture, causing cooling of these parts is called internal cooling.

Theoretically speaking, with a fuel mixture of 14.8 kg air and 1.0 kg gasoline the air lambda number is 1 At this ratio the fuel mixture burns completely. This mixture is called the ideal mixture ratio. Lambda value between 0,7 and 1,25 makes the fuel mix very combustible.

Real mixture properties differ from theoretical ones depending on external conditions (temperature, air humidity, atmospheric pressure) and on the engine operation modes (starting, idling, part load, full load). If the mixture is actually different from the ideal mixture then it is either lean or rich.

Poor mixture has more air in it When the mixture is lean, the engine does not develop full power because of the lack of fuel in the mixture, also the temperature of the engine is high because of low internal cooling. Due to the reduced volume of oil-containing new portion of the fuel mixture, lubrication conditions worsen, which leads to an increased risk of scuffing of the piston-cylinder pair.

Rich mixture contains less air. A rich mixture results in an incomplete combustion of the fuel mixture. Unburned mixture also shows up in the form of smoke from the exhaust silencer.

Design and Function Consider the general construction of a carburetor with an integrated fuel pump.

The carburetor consists of an all-aluminum body, in which there is an opening (Venturi nozzle) with defined internal contours. the diffuser (pos.18. the air drawn in by the engine flows through the diffuser. The smaller the opening of the nozzle, the higher the air throughput and the greater the vacuum in the area of the minimum diameter. In various parts of diffuser there are fuel channels (pos.11, 12), from which airflow sucks fuel. Fuel pump, nozzle system and air-fuel mixture control are either internally built in or externally mounted.

Throttle valve position (pos.9) determines the volume of sucked air and ultimately the power output of the engine. The so-called pulse chamber of the fuel pump through the pulse channel (pos.1) is connected to the internal volume of the engine crankcase. From the reciprocating motion of the piston in the cylinder, in the crankcase there is a successive change in pressure (increased pressure or vacuum). This change in pressure in the crankcase controls the operation of the diaphragm (pos.4) fuel pump. i.e. fuel pump operates forcibly and synchronously with change of pressure in the crankcase depending on engine speed. Fuel is sucked in by the pump diaphragm (pos.4) from the fuel tank through the carburetor inlet connection (pos.2), then through inlet valve (pos.3), exhaust valve (pos.5) of the fuel pump, through the filter screen (pos.6) through channel (pos.10) past the needle (pos.14) through the needle valve into the chamber (pos.16) of the control diaphragm (pos.18) Needle of the needle valve (pos.14) through lever (pos.17) is connected to the control diaphragm (pos.18). Volume located below the control diaphragm through the hole (pos.19) is connected to the outside air (atmosphere).

The entire carburetor also functions by changing the pressure in the crankcase.

At the suction stroke in the diffuser (pos.3. it creates a vacuum resulting in air flow that depends on the engine speed and engine load as well as on the throttle position (pos.9). Fuel is sucked from nozzles (pos.11, 12) from the chamber (pos.16) draws in fuel and mixes it with the flowing air. The fuel is atomized and the fuel-air mixture necessary for combustion is formed. This mixture enters the cylinder. there the individual droplets of fuel. air mixture due to high ambient temperature evaporate.

Since the volume located below the control diaphragm through the hole (pos.19) is connected with the ambient air (atmosphere) the control diaphragm (pos18) moves upwards and the mixture. Simultaneously through the lever (pos.17) it pulls the needle of the needle valve (in the sketch downwards) thus opening the channel and a new portion of fuel enters the chamber (pos.16). as the chamber fills up, the control diaphragm returns to its initial state, the needle valve closes and the fuel portion, which is sucked out through the nozzles, is again present in the chamber. This process is cyclically repeated when the engine is running. Volume of fuel flowing from the nozzles into the diffuser is controlled by the main screw (pos.13) and the idle speed screw (pos.15).(quality) Turning out the screws enriches the air-fuel mixture and turning them back in makes the mixture leaner. in addition, the idle stroke speed can be adjusted by means of the stop screw (pos.), which is located outside and rests on a lever attached to the throttle valve shaft when screwed in. (This screw is not shown on the sketch) With these three adjusting screws it is possible to adjust the engine to obtain the optimum power under any conditions (e.g. high mountains). This is how the carburetor functions in general terms.