Carburetor Needle Adjustment Lawn Mowers

Malfunctioning fuel pump

The most repetitive breakdown is wear and tear of the membrane. As a result, its non-fit. Fuel passages are not sealed at certain stages in the engine cycle. The reasons are as follows:

• You have been working the lawn mower or trimmer for too long without interruption;
• Fueled with low-quality fuel;
• Waste gases enter the pulse channel.

A deformed membrane is fraught with several bad consequences:

• There is not enough gasoline or oxygen in the generated combustible mixture;
• The motor starts after 10 or more unsuccessful attempts;
• The engine knocks, clinks when running, etc.;
• Working piston is deformed.

As a result, the inner space of the fuel pump is contaminated from the side of the impulse channel.

Failure of the adjusting lever

The wear of the contact edge of the lever is a consequence of an incompletely purified fuel, into which sand grains or particles of clay, metal, or other inclusions that are not soluble in liquid hydrocarbons have gotten. There is a problem with fuel injection, the engine does not function without load.

Strainer clogged

Reasons for clogging the mesh filter. poor quality fuel cleaning, damage to the hose and / or delivery head.

The inlet needle is broken

The inlet needle breaks due to metal and stone particles in the gasoline. As a result, the seat of the intake needle does not fit tightly against it, the fuel mixture flows. There is too much air in the fuel mixture created by the carburetor, which can cause the engine to "sneeze" during operation. Finally, the needle may get stuck due to low-quality gasoline, or the unit has been idle for a long time.

Carburetor device

The lawn mower (lawn mower) contains a base. a body made of aluminum, which houses the rest of the parts, working harmoniously as a whole. The carburetor body has a diffuser. a stroke with internal channels through which air is pumped.

Channels branching off from the diffuser stroke deliver fuel, with which the forced air mixes, carrying gasoline vapors with it. Outside the main carburetor compartment are located:

• Jets;
• Mini fuel pump;
• Unit regulating the mixing of fuel with air.

The latter forms the very explosive mixture ignited in the carburetor combustion chamber.

Intake control lever is sticking

Jamming of the adjusting lever is a consequence of its incorrect installation, accidental bending. The contacting face will get the wrong position. This will disrupt additional gasoline injection.

When is carburetor adjustment necessary?

Initially, from the moment the tool was sold, all carburettors were adjusted and tuned at the factory. However, in the process of operation, the settings gradually go astray, and the operating mode changes in accordance with the operating conditions. Signs of a carburetor malfunction may include:

• Too high consumption of gasoline, thick smoke comes from the exhaust pipe;
• The engine power is clearly not enough to perform normal tasks;
• Engine speed "floats";
• After starting, the motor stalls either immediately or after a few seconds;
• The engine cannot be started at all;
• The chainsaw "shoots", there are sharp claps in the tool engine.

It should be noted that during the running-in of a new engine, the carburetor is set to a reduced fuel supply in order to limit the engine power. After the end of the run-in, the fuel supply increases to the nominal value. These adjustments are made using the adjusting screws on the carburetor body (usually two or three).

Design and working principle

A carburetor is a device that mixes fuel (gasoline) and air in specified proportions, followed by feeding the prepared mixture into the engine cylinder. Almost all models of chainsaws are equipped with carburetors of the same type, so the device and principle of operation are the same.

The main structural elements of the carburetor are:

• The body, which is cast from aluminum to reduce weight. Chainsaws constantly have to be moved from place to place, during operation they are held by hands, therefore, reducing the weight of the tool is the primary task of manufacturers;
• A diffuser with an air damper located at the inlet;
• Nozzles, which are valves for metering fuel;
• A sprayer that injects gasoline into the chamber (in the diagrams it is designated as the main jet);
• Fuel (float) chamber.

Figure 1. Diagram of a chainsaw carburetor

The principle of the carburetor can be described as a cycle consisting of the following steps:

• Air damper opens during engine start.
• The piston stroke creates a vacuum in the air channel, as a result of which air enters the diffuser, the amount of which is regulated by the position of the air damper.
• Gasoline flows from the gas tank to the float (fuel) chamber. The rate of its admission is regulated by jets.
• Gasoline and air are mixed in the diffuser, which results in the formation of a fuel-air mixture, which then enters the engine cylinder. The more the mixture enters the combustion chamber of the cylinder, the higher the power and speed on the engine shaft will be.

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

A chainsaw is a useful, and sometimes simply necessary tool for the owner of a private house. It has a high degree of autonomy, can be used in the field, where there is no possibility of connecting to the power supply network. For some craftsmen, the chainsaw is one of the main devices that perform large amounts of work almost daily. Such loads knock down the factory settings that were set for all important engine components.

The operating mode most often changes with the carburetor, which has to be re-adjusted. Without understanding the design and principle of operation of this element, it is impossible to properly adjust it. The question concerns many users who operate chainsaws tightly, so it will be useful to consider it more carefully.

• Design and working principle
• When is carburetor adjustment necessary?
• Adjustment tools
• How to properly adjust the carburetor with your own hands?
• How to set up a China-made saw?

Adjustment tools

To tune the carburetor, you will need a Phillips or slotted screwdriver of different lengths or thicknesses; the size depends on the design of this unit and the features of the engine assembly. It should be noted that some manufacturers make carburetors designed to use special tools.

In particular, special types of screwdrivers may be required to adjust Husqvarna carburettors and other imported tools. It is advisable to clarify this question even when buying a chainsaw, so that you can purchase the necessary additional equipment in advance.

In addition, you will need refined gasoline or acetone to flush and clean the device. They are used to clean the outer surfaces of the carburetor. All internal channels are flushed with kerosene, diesel fuel or white spirit. Before flushing, the carburetor is disassembled, all rubber or plastic parts that may suffer from contact with aggressive chemical compounds are removed.

Open-end or spanner wrenches are used to disassemble the carburetor. Internal canals are washed in specially designated trays, sometimes plastic syringes are used for this.

How to properly adjust the carburetor with your own hands?

After rinsing and completely cleaning the carburetor, assemble it and begin to adjust. First of all, you should understand the purpose of the adjusting screws. The instruction will help with this, but some general points should be considered right away. The most common designations for screws are:

• H. adjusts the state of the main jet, i.E. Adjusts the maximum rotational speed of the motor shaft;
• L. adjusts the idle jets (responsible for the minimum shaft rotation speed);
• T. regulates the idling of the motor. It can also be designated by the letters LA or S, on some models of carburetors it is not at all.

Turning screws H and L clockwise depletes the air-fuel mixture, and counterclockwise enriches it (the amount of gasoline increases). When the screw T rotates, the idling speed of the shaft changes. it increases clockwise, and decreases in the opposite direction.

Figure 2. Carburetor adjustment mechanisms

Before proceeding with direct actions, you should find and carefully study the information on the position of the adjusting screws (the magnitude of the angles of rotation during adjustment). This information is available in the instructions for the chainsaw. Then you need to prepare the workplace. lay the saw on a flat horizontal plane, directing the chain in the opposite direction from you. Detach all covers, remove foam rubber and air filter. At this, the preparatory operations are considered completed, you can proceed to the main part of the work.

Carburetor adjustment procedure:

• Smoothly tighten the screws H and L clockwise until they stop. Be careful not to break the screws. this will cause a complete loss of the carburetor.
• Unscrew both screws one and a half turn.
• Run the engine for 10 minutes and warm it up. This is a necessary moment, since it will not be possible to correctly adjust the carburetor on a cold engine.
• Turning screws H and L, alternately adjust the rotation of the shaft at maximum and minimum revolutions.
• By adjusting the position of the screw T (or it may have another designation), the idle speed of the chainsaw is adjusted. It is necessary to achieve smooth and stable engine operation. It is important to monitor whether the chain is idling or not. If it moves, turn the screw a little more counterclockwise.

You can check the operation of the engine visually and by ear. Too rich mixture will cause thick smoke from the exhaust. When the lean mixture is being fed, a whistling sound is heard while the saw is running. Excessive economy mode is harmful. if the L screw is set to "lean" fuel, there will be problems with starting the engine. If the H screw is set to lean, the saw will noticeably lose power. You can determine the correct setting by the following criteria:

• At idle, the engine does not stall, and the chain is stationary;
• When the engine is running, there is no excessive smoke from the exhaust pipe;
• The engine demonstrates good throttle response (picks up speed quickly when you press the accelerator).

A detailed description of the setting is available in the instructions that come with the instrument in the delivery set. It should be carefully studied, as there may be some features or specific requirements set by the manufacturer and related only to this saw model. If all requirements are met exactly, the performance of the chainsaw will be restored to its original state.

How to set up a China-made saw?

The design of the carburetor on Chinese chainsaws is no different in principle. The order and principle of adjustment also do not differ and are performed in the same order. The only difficulty that may arise during work is determining the purpose of the adjusting screws. Typically the T screw is on the top and the H and L are on the bottom of the carburetor body. One additional screw may be present.

Figure 3. Location of adjusting mechanisms

Usually, their purpose is determined empirically, slightly changing the position and monitoring the result. After the purpose of the elements is clearly defined, further customization is not difficult and is carried out in the usual way.

Chainsaw carburetor tuning is an important and necessary procedure that must be periodically performed to restore the normal operation of the tool. This process does not create fundamental complexity, but it requires the user to be careful, attentive and comply with safety rules. The chainsaw chain is usually not removed, since you will need to observe its position. Therefore, it is important to constantly remember about the possibility of launching it and exercise the necessary caution.

The adjustment should be done smoothly, with small changes in the position of the screws, so as not to cause too sharp changes in the shaft rotation mode. The result depends on the care and thoroughness of the user, and a properly tuned carburetor will extend the life of the tool.

Clogged control cavity

If dirt accumulates in the adjusting cavity, the inlet needle cannot close the hole tightly and a lot of fuel pours into the chamber.

This causes the fuel to over-enrich and the engine starts to malfunction. It is necessary to disassemble the carburetor and clean the cavity of the control membrane.

How the gas trimmer carburetor works and works

It is almost impossible to cover all types of carburetors produced by manufacturers of gas trimmers. But, since the design of this module, as well as its principle of operation, is largely similar between different models, it is possible to make a generalized description of the processes occurring in the carburetor. This information will allow the user to understand the principles of operation of the device, to eliminate the malfunctions that have arisen and to operate it correctly.

The carburetor trimmer is based on a one-piece aluminum body. Below is a diagram of this block.

At the bottom of it, there is a diffuser, which is also called a Venturi nozzle (18). Air is sucked in through this nozzle by the motor.

The top of the diffuser contains the fuel channels (11,12). Through these channels, the flow of air draws in gasoline. The fuel pump itself, jets and the system used to regulate the supply of a mixture of fuel and air can be built-in or installed externally.

The throttle valve (9) controls the amount of air sucked into the carburetor. Its amount affects the power that the engine develops. The damper (7) is used for cold starting. It must be closed if you are going to start the unit. After the engine has started, it must be opened, otherwise, the engine will immediately stall.

The impulse channel (1) connects the impulse chamber of the pump to the crankcase of the engine, namely, to its internal volume. The piston located in the cylinder, making reciprocating movements, successively changes the pressure in the crankcase (vacuum or pressure increase). The pressure drops force the diaphragm (4) to move. Therefore, the pump operation is synchronized with the engine operation.

The suction of gasoline from the tank occurs precisely with the participation of the membrane (4). Gasoline enters the carburetor through the union (2). Further, its path lies through the inlet valve (3), the exhaust valve (5), through the mesh filter (6), the fuel channel (10), passes the needle (14) and fills the chamber (16), which has a control membrane (18).

The valve (14) is connected to the diaphragm (18) by means of a lever (17). The cavity, which is located below the membrane, is connected to atmospheric air through the hole (19).

The device functions as follows.

• A vacuum is generated in the diffuser during the suction stroke. This fact causes air leaks. The position of the throttle valve (9) determines the amount of air entering the carburetor chamber, as well as the engine power and the number of revolutions.
• At this time, fuel from the chamber (16) is sucked in through the jets (11,12), after which it is mixed with the flowing air. Gasoline, mixing with air, begins to spray. Thus, an air-fuel mixture is created.
• The finished mixture enters the cylinder, where it is compressed by the rising piston and ignited at its highest point from the spark generated by the spark plugs.
• Since the volume under the control diaphragm (18) is connected to the ambient air through the channel (19), the diaphragm goes up, opening the valve (14) by means of the lever (17). After opening the valve (14), a new portion of fuel enters the chamber (16).
• After the chamber (16) is full, the diaphragm (18) returns to its original position, and the valve (14) closes.

Further, when the motor is running, all the above processes are repeated. A screw (13) is used to adjust the amount of fuel entering the diffuser through the nozzles. The screw (15) is also used to adjust the idle speed. When the regulators are twisted, the fuel mixture is enriched, and when the regulators are twisted, the mixture becomes lean. Also, in some carburetor models, you can adjust the idle speed of the engine with a quantity regulator. It is usually located outside and, when twisted, abuts against a lever attached to the throttle shaft.

Thus, using 3 adjusting screws, you can achieve maximum performance of the engine, as well as adjust its smooth operation at any ambient temperature, and even in mountainous areas.

Intake Adjust Lever Problem

This problem can occur if the adjusting arm is not properly installed or if it is bent before installing. As a result, the contact surface takes the wrong position, which disrupts the additional fuel supply.

Throttle and choke shaft wear

The air and throttle shaft can wear out for the following reasons:

• Insufficient and improper maintenance of the air filter;
• The air filter is damaged;
• The air filter is not suitable for this machine.

Due to the ingress of poorly cleaned air, the shaft wears out and may break. Broken shaft parts can enter the combustion chamber or crankcase and cause serious damage to the entire piston system.

To eliminate problems with air purification, it is necessary to replace the defective filter or flush the existing (serviceable) one. The filter must be washed in soapy water and dried.

Deformation of the control diaphragm

The membrane can undergo deformation during prolonged operation of the unit and when using aggressive fuel.

Failure to perform normal adjustment due to a defect leads to:

• Damage to the piston;
• Difficulty starting up;
• Depletion of fuel;
• Improper engine operation.

Common carburetor malfunctions

Failure of the trimmer carburetor occurs due to the use of poor quality gasoline, a damaged air filter and the accumulation of dirt in the chamber of this unit. Most often, it is quite possible to repair the carburetor with your own hands. Listed below are typical lawn mowers carburetor malfunctions.

Carburetor adjustment

Flush the air filter before adjusting the carburetor. It is recommended to rinse it after every 10 hours of operation. After that, you can start adjusting. The photo shows the PRORAB-8406 petrol trimmer carburetor as an example. The numbers indicate the adjusting screws that we will use.

PRORAB-8406 petrol trimmer carburetor adjusting screws

Purpose of adjusting screws:

• Fuel mixture adjustment screw.
• Idling adjustment screw.
• Maximum speed limiting screw.

Start a lawn mower and wait for it to warm up.

Fuel ratio

I read somewhere that if different mixing ratios are indicated in the operator’s manual for the lawn mowers and on the oil canister, the proportion specified in the manual should be used.

For a long time he did this. excess oil flowed from the engine onto the gas tank and carbon deposits were constantly formed on the candle, since the manual indicated the proportion for the run-in engine 1:25, and on the canister. 1:50. After switching to a ratio of 1:50, the appearance of oil drips stopped. The candle continued to burn, but at a lower intensity (the carburetor was not yet adjusted).

Until now, some users of gasoline-powered tools determine the proportion of the fuel mixture "by eye". If the amount of oil is lowered during the preparation of the mixture, after a while an extraneous sound may appear immediately after starting the engine, gradually disappearing during warming up, and the engine will stop with a sharp jerk. Continued use of the trimmer in this mode will lead to its failure.

Maximum speed limitation

After adjusting the fuel mixture and low speed, check how the lawn mower engine will run at maximum speed. If necessary, limit the maximum RPM to the required level with the # 3 hollow screw. Loosen the retaining nut and turn in the screw to decrease maximum RPM or turn to increase it. Tighten the nut after adjustment. The maximum RPM setting is necessary to protect the trimmer motor from overheating and to be able to use the start key lock to reduce right hand fatigue.

In the future, it may be necessary to adjust the trimmer carburetor. For example, if the engine starts to rev poorly when running at full load, loosen screw # 1 another quarter turn. If starting is difficult, increase idle speed. Both weather conditions and the quality of the fuel mixture can affect the operation of lawn mowers. Vibration can cause the adjusting screws themselves to turn.

Lawn mower or trimmer

A trimmer is a broader concept than a lawn mower (lawn mower), as it can also be electric. A petrol trimmer and a lawn mower are one and the same.

Some authors claim that the trimmer is a weaker tool than a more powerful lawn mower, which can be used for mowing shrubs. Personally, I have a tool with a maximum power of 1.7 kW and is capable, as stated in the instructions, of mowing small shrubs up to 10 mm thick. The user manual is called "Petrol trimmer.".

From personal experience

Fuel supply adjustment

Start slowly turning the fuel mixture adjustment screw until the engine starts to stall or stalls if you do not have time to catch the moment. After that, unscrew the screw a quarter of a turn if the engine has not stalled, or half a turn if it stalled. Start the stalled engine. Check by opening the throttle as the engine picks up speed. Continue to unscrew the screw No. 1 by a quarter of a turn until the engine starts to accelerate steadily during gas flow. This will be the moment of the most economical stable engine operation. For the PRORAB-8406 petrol trimmer, the adjusting screws are turned clockwise, unscrewed. against, for some other brands the lawn mower can be the other way around.