How Does A Chainsaw Carburetor Work

How a chainsaw carburetor works detailed description

Many people know how a two-stroke carburetor works on tools such as chainsaws, lawn mowers, and gas generators. However, this knowledge is only generalized, and when it becomes necessary to repair or regulate the carburetor, a bunch of questions immediately appear, the answers to which can be found yourself, if you understand thoroughly what the principle of the chainsaw carburetor is based on. It is in this that you have to figure out how the carburetor of chainsaws of different brands works.

What does a chainsaw carburetor consist of?

The considered units of modern chainsaws differ in design from the old-style devices. over, this difference lies not only in the design, but also in the principle of action. But first things first. First, we will find out the main components of the mechanism, and then we will understand the principle of the functioning of the chainsaw carburetor.

Structurally, the chainsaw carburetor can be divided into three parts:

• Fuel suction chamber from the gas tank. This chamber is connected not only with the gas tank through the fuel line, but also with the design of the crank mechanism. This part consists of two fittings, a membrane for pumping fuel, two valves, a filter and a transport channel.
• The chamber for the accumulation of the fuel mixture and its flow to the idle, medium speed and maximum speed channels. This chamber consists of a needle or needle valve, a diaphragm for opening the needle, a fuel accumulation chamber, adjusting screws, a maximum speed flap, and XX and medium speed channels, which are always open
• The working area is the main area where air and fuel mix and flow into the combustion chamber. The main working elements of the working area include dampers (air and throttle), as well as a diffuser, in which fuel and air are mixed

How does a chainsaw carburetor work. features of air intake

The principle of operation of the chainsaw carburetor also includes the supply of an air mixture to the device. As you understand, it is not clean fuel (oil with gasoline) that enters the combustion chamber, but the fuel mixture. oil with gasoline from the tank and air that preliminarily passes through the filter element.

So, the air passes through the filter, and enters the device through the membrane number 7.

The air damper 7 during cold start is almost completely closed, as shown in the diagram. Through it there is a slight intake of air into the system. Air enters the diffuser 16. Number 12 denotes the idle and medium speed channels or jets. These channels are interdependent, that is, the medium speed channel is transitional from idle. These channels are constantly open, so fuel in an appropriate dosage enters the diffuser, where it mixes with air, heading towards the cylinder.

Number 15 denotes the maximum speed channel, which consists of a valve with a rubber base. Through this valve, fuel is supplied in one direction. into the diffuser chamber. Further, the throttle valve 8 enters the system, the movement of which depends on the force of pressing the gas unit. When starting, valve 8 is in a vertical position, so the chainsaw operates only on the fuel mixture coming from channel XX. At the same time, the amount of air is insignificant, since the damper 7 is also open a few millimeters. When the trigger of the tool is pressed, the flap is deflected by 10-15 degrees, as a result of which the fuel mixture is supplied from the medium speed channel 12 in the diagram above.

When the sawman starts sawing wood, the number of revolutions increases to the maximum, so the shutter moves up to 90 degrees from the initial position. There is an increase in the amount of fuel, which contributes to the acceleration of the combustion of the fuel mixture.

In order to fill the chamber 14 with a fuel mixture of gasoline and oil, which enters through the channel closed by the needle, it is necessary to create a vacuum, due to which the membrane 13 is pulled inward, thereby acting on the stem. The vacuum in the chamber 14 is created during the jerking of the starter handle when the tool crankshaft moves. The piston moves up and down when the starter handle is “blinked” or “poked”, which provokes the creation of pressure inside chamber 14. As a result, the chamber is filled with fuel, which flows through the corresponding channels into the diffuser, mixing with air, and heading into the cylinder.

After the engine of the unit is started, the piston will begin to move under the influence of the combustible mixture, therefore, the vacuum in the chamber is formed constantly, which actually provokes the deflection of the plate 13, which acts on the needle valve through which fuel enters the main chamber of the carburetor of the chainsaw.

Actually, this is the principle of operation of a membrane-type chainsaw carburetor, the functioning of which does not depend in any way on the angle of its location. Knowing the design and principle of operation of the unit, you can start setting up, cleaning and adjusting.

Why is a chainsaw carburetor called a diaphragm

Before proceeding to consider the principle of operation of a chainsaw carburetor, you need to figure out why they are called membrane. The diaphragm (diaphragm carburetor) is an advanced model that can work in any position. This is very important, as a chainsaw, like lawn mowers, is not operated in one position. Therefore, membrane carburetors are capable of working in any position, which is their main difference from devices of an outdated design or an old model.

If a membrane is used in the carburetor of the new model, then in the models of the old model, which are used on a chainsaw such as Druzhba, there is a float chamber. It is in the float chamber that gasoline of the corresponding volume accumulates. When the float goes down when gasoline is consumed (the chamber is emptied), the needle moves along with the float, which opens the fuel supply hole to the float chamber.

In this case, the normal operation of the old-style carburetor is ensured under one simple condition. it must be in the appropriate position. When the device is moved to the side 90 degrees or more, the float will move, and therefore the needle will block the fuel holes. That is why old-style chainsaws are designed only for operation in one position. The unit itself is in one position, and depending on the type of work performed (cutting down a tree or sawing a log), the position of the tire is adjusted.

Knowing how the Druzhba chainsaw works, you can begin to consider the principle of operation of the carburetor of modern units, in which there is no mechanism for moving the tire (changing the angle of its position).

The principle of functioning of the carburetor on a two-stroke engine of a chainsaw

We continue to understand step by step with the principle of operation of the carburetor of two-stroke engines of chainsaws. Such knowledge will be useful not only for beginners, but also for those who wish to independently repair, adjust or adjust the carburetor. It is also necessary to know the principle of operation in order to understand why certain defects arise in the operation of the instrument.

So, the fuel passes through the filter element, and reaches the needle, which is indicated in the diagram below as number 11.

Now we have to figure out the principle of operation of the second membrane of the carburetor, which is shown in the diagram at number 13. Under the membrane is a protective plate with an opening through which air enters. The diagram below shows air movement.

Number 14 on the diagram shows the fuel in the carburetor chamber. However, it will not enter this chamber until the needle 11 opens (moves down). To move the needle, a membrane 13 is used, which is connected to the needle through a rocker arm. The spring mechanism near the rocker arm is designed to return the membrane 13 to its original position.

It is worth noting that the membrane is made of a flexible material, so it bends under the influence of the rod from the rocker arm. To open the needle, the membrane must move upward, thereby acting on the stem, and through the rocker arm, the needle moves to the lower position, which will entail the flow of fuel into the chamber.

To understand why the membrane 13 bends or moves, due to which the needle opens for fuel to enter the chamber, it will also be necessary to find out the features of air flow into the mechanism.

How does a carburetor work on a chainsaw. we deal with the fuel supply to the device

So, the device under consideration on a modern chainsaw has a simple principle of operation, which is based on vacuum. Probably, when repairing a chainsaw, more than once every sawyer asked himself the question why there was no fuel pump on the unit. On such a small unit, there is simply no place to install a pump, and the carburetor itself performs its fuel supply function. To understand how the chainsaw carburetor works, let’s first consider the features of the fuel supply to the mechanism.

How is fuel supplied in modern chainsaws with membrane carburetors? In modern chainsaws, fuel is supplied to the carburetor through a special membrane, which is indicated in the diagram below under the number 4.

In the diagram, this membrane is indicated as a dotted oval. Its movement occurs due to the vacuum pressure. A quite pertinent question arises as to where this rarefaction comes from. Let’s consider in detail why we will rely on the diagram below.

The fitting at number 1 is connected to the gas tank, which is located below the level of the carburetor. According to the law of physics, fuel cannot enter the carburetor according to such a scheme. For this, in the design of the device under consideration, there is a fitting 2 (it can also be represented as a hole, which depends on the model of the tool, but the principle of operation of the chainsaw carburetor is identical). Through fitting 2, pressure enters the carburetor, the intake of which takes place through the channel from the KShM chamber (crank mechanism). The diagram is shown in black line.

From the KShM chamber to the carburetor chamber through the nozzle 2, there is an alternating supply of air under pressure, the cycle of which depends on the speed of rotation of the tool crankshaft. That is why, before starting the chainsaw, you need to initially make several movements of the starter (which drives the crankshaft) without ignition, in order to pump gasoline into the combustion chamber, and only after that start.

When a vacuum pressure is created by membrane 4, valve 3 is opened and closed alternately. Fuel enters the carburetor chamber and is directed to the inlet valve number 5. Valve 5 opens depending on the pressure generated, but not by the membrane, but by the fuel itself. Further, the fuel enters through the filter element number 6, and moves already cleaned up to the needle. The further scheme of operation of the chainsaw carburetor is described in the next section.

What type of carburetor is used in modern chainsaws

All modern chainsaws use membrane-type carburetors. They were developed by German designers from the world’s leading manufacturer of chainsaws, Stihl, in the mid-50s of the last century and revolutionized the design of chainsaws.

Before that, float carburetors were used, which could only work when the chainsaw was in an upright position or at an inclination of no more than 45-50 degrees. New membrane devices made it possible to operate the chainsaw even in an inverted position.

Membrane carburetor from different angles.

How the carburetor of a modern chainsaw works

The carburetor on a chainsaw performs the same functions as on any device with an internal combustion engine, from a moped to a car. The difference is that the chainsaw is a hand tool. Therefore, every unit, including the carburetor, should be as compact and lightweight as possible. To do this, use the simplest design and lightweight aluminum alloys with ferrous metals or magnesium.

How does a membrane-type chainsaw carburetor work?

The diaphragm carburetor is assembled from 20-30 parts, depending on the model. They include fastening screws and gaskets, as well as 17 functional elements. The basic device is shown in the diagram below.

Chainsaw carburetor operation diagram

• Connection for a hose from a gas tank for supplying gasoline.
• The channel through which fuel is pumped when the primer (suction) button is pressed when starting a cold engine.
• Inlet valve that closes when the chamber is full.
• Suction membrane.
• Membrane chamber fuel outlet valve.
• Strainer.
• Rotary damper that regulates the air supply from the air filter.
• Throttle (gas) valve that regulates the supply of the fuel mixture to the combustion chamber.
• Fuel supply channel.
• Idle speed adjustment screw.
• Needle, regulating the amount of fuel-air mixture.
• Idle speed jet.
• Membrane that determines the position of the needle and the amount of the incoming mixture.
• Fuel chamber.
• Main jet.
• Diffuser chamber where gasoline and air are mixed.
• Working speed adjusting screw.

The carburetor allows the engine to operate in 3 modes:

• Cold start.
• Idle speed.
• Working revolutions.

During a cold start, the primer (suction) button is manually pressed. At the same time, the diaphragm of pump 4 is compressed and opened. A vacuum is created, and due to it there is a direct pumping of gasoline from the tank into the fuel channel of the carburetor. This makes starting a cold engine faster and easier after a long idle period.

Then, when the engine is running, a vacuum is created already due to the piston stroke in the combustion chamber. Fuel begins to be sucked from the gas tank into the carburetor through the nozzle 1. This happens until the chamber 14 is filled. When filling, the membrane changes its position due to pressure and presses on the needle 11 through the rocker arm. The needle rises and shuts off the fuel supply. This eliminates the overflow of fuel into the diffuser and then into the combustion chamber.

After gasoline from chamber 14 goes into the diffuser and then into the combustion chamber, the membrane bends, changing the position of the needle, and the fuel supply resumes until chamber 14 is full.

The cycle repeats itself. Thus, in the chamber 14 there is always the amount of fuel necessary for the engine operation and tightness, which ensures the flow of fuel into the combustion chamber due to the vacuum from the piston stroke.

In idle mode, the damper is closed, and the minimum amount of fuel enters through the slot at the bottom of the damper. The amount of incoming fuel, and therefore the idle speed, is regulated by screw 10.

There are carburetor models where the idle speed is controlled by the throttle position. In this case, the adjusting screw does not regulate the fuel supply through the channel, but the position of the damper.

To consolidate the information read, we recommend that you look at the corresponding one, the author of which tells and shows in detail about the structure and principle of operation of the diaphragm carburetor of the chainsaw. In the course of the story, the author covers the main problems, malfunctions. Quite useful on this topic.

Float carburetors

The principle of operation of membrane and float carburetors is the same. The difference is that older carburetors used a float instead of a membrane. It is a sealed lightweight container made of copper alloy with a central steel axis. The lower part of the axle fits into the bushing at the bottom of the chamber and serves to hold the float. The upper is made in the form of a needle.

The photo shows a disassembled float-type carburetor, a Druzhba chainsaw, in the middle (in the form of a rocker of two barrels) there is a float.

When the chamber is filled, the float floats up, the needle shuts off the fuel supply, as in the diaphragm version. But if you put the chainsaw with a float carburetor on its side, the float will not be able to float up to the end and the needle will not cut off the fuel supply. The carburetor will start to “overflow”, as a result the engine will stop working normally. The spark plug may be flooded when the spark disappears and the engine stalls completely.

Unlike modern chainsaws, the position of the cutting attachment was adjusted in older models. The engine itself could remain in a stable position, vertically (candle above), and the bar with the chain could be turned horizontally to felled a tree or vertically to cut a lying trunk.

We recommend reading a more detailed analysis of the device of float carbs in our article about carburetors of the Druzhba chainsaw.

In more detail, the device and principle of operation of the float carburetor is disassembled in our article on the Druzhba 4 chainsaw carburetor.

However, the working position of a chain saw with a float carburetor is always limited, which reduces the possibilities when working. A chainsaw with a membrane carburetor can work in any position, even upside down, which is important when filing bitches at a height and working in hard-to-reach places.

The reliability of both options depends on the quality of the materials used and the workmanship. The membrane should be made of a plastic that is resistant to gasoline and retains elasticity for a long time.

Floats failed due to loss of tightness and oxides in the channel when the needle began to get stuck in it.

The diaphragm carburetor is best suited for chainsaws. The principle of operation itself has remained unchanged for more than half a century, but the quality of these devices is constantly improving. They become lighter, more compact, and form a better fuel mixture. As a result, the internal combustion engines of chainsaws with modern carburetors consume less fuel and emit less harmful exhaust gases into the atmosphere.

The principle of operation of the chainsaw carburetor

Before you adjust the carburetor on a chainsaw, you need to understand the principle by which it works.

• When the engine starts, the air damper located at the bottom of the housing opens.
• A vacuum is created in the air duct and float chamber, caused by the piston stroke, as a result of which air flow is sucked through the diffuser.
• The suction rate of the air flow is adjusted by the position of the air flap.
• Gasoline through the inlet fitting from the gas tank enters the float chamber.
• The speed of passage of gasoline from the chamber to the diffuser is regulated by means of jets.
• Gasoline is mixed with air in the diffuser.
• The prepared air-fuel mixture enters the intake channels, from where it is directed to the working combustion chamber of the cylinder.

The main malfunctions of the carburetor on a chainsaw

It should be understood that the dimensions of all the holes are very small. Even the smallest contamination can block the flow of air or fuel, which is why filter elements are installed at the inlets. Unfortunately, they do not always cope with the task at hand. Chainsaw carburetor malfunctions are indicated by the following symptoms:

• High gas mileage and thick exhaust smoke;
• The engine "does not pull";
• Floating revolutions;
• The motor starts, but stalls immediately or after a few seconds;
• The motor does not start at all.
• The chainsaw shoots the carburetor

All these malfunctions are a sign of a violation of the carburetor adjustment on the chainsaw, or it is dirty. Hence the need for adjustment, cleaning or repair. How to do this. consider below.

How to properly adjust the carburetor on a chainsaw with your own hands

Chainsaw carburetor factory settings provide optimal parameters for fuel and air intake. But in the process of work, they can go astray due to vibration. a shift of even ¼ of a turn for any of the screws can lead to a serious change in the parameters of the preparation of the air-fuel mixture and it is necessary to adjust the carburetor of the chainsaw.

The carburetor of the chainsaw is adjusted using three screws marked H (High), L (Low) and S. The last screw, depending on the brand and manufacturer, may have other names, for example T or LA.

• H: responsible for the operation of the main jet and regulates the maximum speed.
• L: adjusts the position of the idle jet and allows you to adjust the low speed.
• S / T / LA: intended to adjust the idle speed of the motor.

To know how to properly adjust the carburetor on a chainsaw, a technical data sheet is required. it contains information about the angles of rotation of the adjusting screws. After that, we go directly to the adjustment. By the way, here you need a screwdriver to adjust the carburetor of the chainsaw or a regular flat screwdriver:

• Place the chainsaw on a flat surface, preferably a table or something similar. IMPORTANT: The chainsaw must be positioned so that the tire points in the opposite direction. The engine must be turned off.
• Use a wrench or a screwdriver to unscrew the fasteners of the housing cover and remove it to get to the carburetor.
• Remove the air filter that covers the chainsaw carburetor. The manufacturer can install a foam rubber shock absorbing insert on top of the carburetor. it must also be removed.
• Chainsaw carburetor tuning now begins. Screws L and H must be tightened up to the stop. Roll them in slowly and carefully so as not to break.
• Loosen both screws about 1.5 turns.
• Start the engine and let it run for about 7-10 minutes so that it warms up well. on a cold engine, you will not be able to adjust the carburetor of the chainsaw.
• After the engine has warmed up, set it to work at medium speed.
• Slowly begin counterclockwise to tighten the idle screw. You need to twist until the motor runs smoothly. In case the engine starts to stall, it is required to continue adjusting the carburetor of the chainsaw and gradually return the screw clockwise.

After the carburetor of a Chinese-made chainsaw or any other has been adjusted, it is necessary to "drive" the motor at different speeds.

The main components of the carburetor are:

• Housing. Made of aluminum for lightweight construction, it has a one-piece shape. The housing contains a diffuser, an inlet connection, an impulse channel, a main screw and an idle screw, a damper that regulates the air supply, and other elements.
• Diffuser. Located at the carburetor inlet.
• Jets. Special valves by means of which the amount of fuel is regulated.
• Spray.
• Float chamber.

Chainsaw carburetor device

Almost all chainsaw models use an identical carburetor design. As an exception, the carburetor of some very cheap Chinese chainsaw can be called. there may not be some parts, and most of the nodes are made from very cheap materials.

An approximate diagram of a chainsaw carburetor

Gasoline does not flow into the chainsaw carburetor

If the fuel does not enter the standard chamber, then this may indicate several breakdowns at once. The first step is to check the air and fuel filters. During long-term operation of the saw, these elements absorb a large amount of dust, which further prevents the infiltration of clean air and fuel. A slightly dirty filter can be cleaned with gasoline, but if the part is clogged with a lot of dust, then it will need to be replaced.

Another reason for the malfunction is the needle. This part sticks, especially in Chinese-made chainsaws. To fix the problem, in most cases it will be enough just to move the needle.

If no fuel enters the chamber, the saw owner should inspect the tool seals. After several months of using the tool, these parts lose their tightness. Over time, they begin to leak gas, as a result of which the instrument stops starting. Repair is carried out by replacing oil seals.

The breather plays an important role when starting the saw. It is located near the saw’s gas tank cover, and performs 2 tasks at once. it maintains optimal air pressure and does not allow fuel to leak out. To check the breather, you will need to turn off the fuel pipe and see how much gasoline flows out. If it does not leak at all, then the standard breather is clogged with debris and dirt. In this case, you will need to clean the element and reinstall it.

If fuel does not enter the chamber, then you need to check the fuel line. Most often, a Chinese hose is used to complete a budget-class tool, which eventually loses its tightness. In this case, it will be necessary to replace the line, paying special attention to the tightness of the channel joints.

Chainsaw carburetor device

Most modern chainsaws are equipped with nearly the same carburetors. They practically do not differ from each other, and work according to a similar principle. The only difference between cameras from different manufacturers is the material from which they are made. In expensive American, Swedish and German chainsaws, cameras are made of reliable alloys, on which protective coatings are applied. Cheap Chinese and Korean chainsaws are equipped with nodes made from cheap materials.

Each carburetor consists of the following elements:

• Aluminum body with one-piece construction. Inside the body there is an inlet fitting, a main screw, an impulse channel, a bolt for adjusting the engine when idling;
• Throttle valve. it is responsible for adjusting the amount of air required to enrich the fuel mixture;
• Diffuser. located next to the camera inlet;
• Sprayer. designed to supply the fuel mixture directly to the carburetor chamber;
• Float chamber. there is a float in it, which is triggered in the event of an insufficient amount of fuel;
• Jets. are valves that are responsible for adjusting the amount of fuel.

This chain saw carburetor circuit is as simple and effective as possible. In some models of gardening tools, it can be supplemented with additional pipes, oil seals or filters.

The principle of operation of a chainsaw carburetor is quite simple. When the engine starts, the air damper located at the bottom of the housing opens. In this case, a vacuum is formed in the float and air chambers, caused by the movement of the piston. As a result, the standard diffuser is triggered, which begins to suck in air. The amount of intake air depends on the opening of the damper. When the piston is triggered, fuel begins to flow into the chamber through the inlet fitting. Its quantity and flow rate depend on the position of the nozzles.

Subsequently, the fuel in the air chamber begins to mix with air. After that, the finished air-fuel mixture passes through the intake valves, from where it is sent to the combustion chamber of the saw engine.

Chainsaw carburetor

The chainsaw carburetor is the element that mixes the air / fuel mixture. Not only the stability of the engine, but also the speed of the entire chainsaw depends on the condition and serviceability of this important unit. In this regard, each owner of a garden tool should study the design of the carburetor, as well as familiarize himself with the rules for its maintenance and repair.

Chainsaw carburetor adjustment. what a beginner needs to know?

Initially, all adjusting bolts are in the factory positions. this ensures that the optimal amount of fuel and air is sucked in. However, due to prolonged use of the saw in difficult conditions, the factory settings of its carburetor may be violated. Even a slight movement of one of the bolts by 1/5 of a turn will seriously damage the saw motor. In this regard, the operator must constantly monitor that the adjusting bolts are in the optimal, factory-set, positions.

If for some reason the work of the node has been disrupted, then it will need to be reconfigured. For this, 3 adjusting bolts are provided in the assembly device. The first of them is marked with the letter H. it is needed to tune the engine of the chainsaw when operating at maximum speed. The second screw marked L is used to adjust the motor when running at low rpm. The third screw can be labeled T, S or LA. Its task is to configure the internal combustion engine when operating in idle mode.

Chainsaw carburetor tuning must be carried out with a completely serviceable engine. Immediately before adjustment, you will need to inspect the air filter, and, if necessary, clean or replace it.

How to flush the carburetor of a chainsaw?

To clean the assembly from stubborn dirt, it is best to use a product that is available commercially in pressurized cylinders. The kit includes a dispenser and a long thin tube that allows you to spray the product in any hard-to-reach places.

It must be remembered that cleaning the carburetor on a chainsaw is carried out using flammable chemicals. You need to work with them in a special protective mask and only in well-ventilated areas.

To clean the carburetor on a chainsaw, the unit will need to be partially disassembled. The throttle valve, adjusting screws, housing and other parts of the carburetor will need to be rinsed with a bottle cleaner and set aside until completely dry. Once all the elements are dry, the unit can be assembled and installed back on the chainsaw.

How to properly adjust the carburetor on a chainsaw?

Place the tool on a firm, level surface to set up the assembly. It is best to adjust the carburetor of the chainsaw in a place protected from dust and moisture.

The node setup process should look like this:

• First you need to unscrew the fastening bolts and remove the protective saw body. This will make it possible to inspect the carburetor and, if necessary, clean it;
• Next, you need to remove the standard air filter of the tool. If the saw is equipped with an additional foam insert, then it must also be removed;
• After that, you need a screwdriver, which you need to tighten the bolts marked H and L clockwise until they stop. This must be done very carefully so as not to break the bolts;
• Then both screws should be unscrewed 1.5 turns in the opposite direction;
• Next, you need to start the chainsaw engine and let it run for about 7 minutes;
• As soon as the engine cylinder heats up, you will need to start turning bolt L until the internal combustion engine starts working at maximum speed. Immediately thereafter, the bolt must be turned 1/4 turn in the opposite direction;
• Then you need to adjust the operation of the motor at high speeds. To do this, you need to connect an electronic tachometer to the engine, and start turning the bolt H until the readings on the instrument panel coincide with the instructions for the recommended maximum speed in the instructions for the saw;
• In the end, it remains to adjust the operation of the internal combustion engine of the saw at idle speed. To do this, slowly turn the bolt T against the clock hand until the motor runs stably and without dips. If the engine starts to stall, then the T bolt should be turned in the direction of the clock hand.

To adjust the carburetor on a chainsaw, you should work as accurately as possible with the adjusting bolts. Excessive tightening of the screws will lead to increased stress on the engine and other important parts of the garden tool.