How to adjust the carburetor on a Stihl lawn mower

Trimmer carburetor. How to properly adjust the trimmer carburetor.

On trimmers, in addition to electric motors, gasoline internal combustion engines are installed. This mechanism requires special attention to itself, since if it is incorrectly configured, it will either refuse to work, or it will work intermittently and loss of power. Basically, engine tuning is about adjusting the fuel flow, and this is done using the carburetor trimmer.

The standard design of any gasoline trimmer necessarily includes a fuel system, the basis of which is the action of a regular carburetor. Its structure and initial principle of operation are almost the same for all lawn mowers, regardless of their design features and purpose..

The lawn mowers carburetor consists of an all-metal aluminum housing that protects the internal components of the unit from moisture, small debris and dust. In the lower part of the body there is a built-in diffuser, the second name of which is “Venturi nozzle”. The main function of this standard part is to supply air in the amount required by the fuel unit to enrich the fuel. A diffuser works according to a simple principle: the smaller its diameter becomes, the more intensively the air is sucked in. This is due to the fact that in the area of ​​the smallest diameter, the level of air vacuum becomes maximum.

The upper part of the built-in factory diffuser is pre-equipped with fuel pipes, through which, under the influence of air, the fuel mixture is drawn in. The rest of the carburetor parts: standard adjusting screws and a fuel pump, can be located both inside and outside the carburetor.

The device of the carburetor of lawn mowers includes a throttle valve, the main task of which is to regulate the volume of intake air. The larger the amount of air, the higher the rated power of the trimmer power unit. Another function of the damper is to facilitate cold starting of the engine. If this is the first time the mower is started after a long period of inactivity, the shutter must be closed. Immediately after starting the engine, the part must be opened, otherwise the internal combustion engine will stall.

The carburetor for the trimmer is equipped with an impulse channel that connects the internal cavity of the engine crankcase with the impulse chamber of the pump. The piston located in the engine cylinder creates reciprocating movements, which leads to gradual changes in pressure inside the crankcase. At the same time, the membrane is set in motion. Thus, the action of the pump is fully synchronized with the operation of the power unit..

The diaphragm of the standard carburetor takes an active part in the suction of fuel. It enters the fuel unit through the fitting. The fuel then passes through the integrated inlet and outlet valves, then through the strainer and fuel pipe. The fuel then flows next to the needle and gradually fills the chamber equipped with the control diaphragm..

The standard carburetor trim valve is connected to the diaphragm using a lever. Below the built-in membrane there is a cavity into which air is sucked in through a special opening.

The lawn mower carburetor works on this principle in stages. This ensures continuous operation of the fuel unit and uninterrupted fuel supply to the cylinder of the standard power unit..

When is the carburetor setting of the household trimmer required? Adjust the built-in trimmer carburetor when:

  • running in a new engine, during which from 4 to 5 liters of fuel mixture were used;
  • sudden changes in weather;
  • changes in air pressure – for example, when the lawn mower is often used in mountainous areas;
  • long-term simple trimmer;
  • intensive growth of loads on the power unit of lawn mowers;
  • arbitrary unscrewing of the built-in adjusting screws of the carburetor – this causes increased vibration of the internal combustion engine;
  • changes in the quality of the components of the fuel mixture;
  • pouring fuel with a carburetor, resulting in an increase in fuel consumption;
  • the regular appearance of a thick layer of resinous deposits and carbon deposits on the surface of the electrodes of a standard trimmer spark plug;
  • starting the engine and its arbitrary shutdown or a slow set of revolutions;
  • lack of fuel flow into the cylinder of the power unit;
  • an increase in the volume of emitted waste gases.

The lack of timely adjustment of the carburetor threatens with a serious breakdown of the trimmer, up to the complete failure of its factory engine.

Do-it-yourself lawn mowers carburetor adjustment. Periodic adjustment of the trimmer carburetor should be performed on a serviced and fully serviceable power unit. Before starting the procedure, the operator must thoroughly rinse the internal combustion engine parts and inspect its CPG for burrs or other defects. In addition, you will need to clean or change the spark plug, as well as rinse the filter elements in the lawn mowers structure..

The lawn mower engine must be running under a certain load when adjusting the carburetor. It is best to install a cord of the appropriate diameter or cutting knives on the trimmer..

After installing the cutting elements, the operator should start the internal combustion engine of the trimmer and leave it to work for about 10 minutes. If, during the operation of the power unit at idle, it was noticed that the cord or knife rotated, then it is necessary to reduce the speed generated by the motor. To do this, turn the lower adjuster, often marked with the letter “T”, to the left, until the installed cutter comes to a complete stop. Further configuration of the fuel assembly is as follows:

  • The “L” regulator, located on the right, is responsible for enriching the fuel mixture with air when the engine is running at low revs. The position of this screw must be adjusted first. To do this, the operator will need to achieve maximum engine speed when idling – to do this, turn the screw “L” one by one to the right or left. As soon as the maximum speed is reached, the screw will need to be turned 1/2 turn to the left;
  • The screw “T” or “LA” is required to adjust the idle speed. While turning it to the left, the speed of the power unit will decrease, and when turning to the right, accordingly, it will increase;
  • The regulator “H”, provided on the left, is responsible for enriching the fuel mixture with air when the internal combustion engine trimmer is running at high rpm. This screw is also needed to adjust the engine power and the amount of fuel consumed. Its position is adjusted by turning the screw to the right or left side until the maximum permissible engine speed is reached. After that, the screw “H” will need to be turned 1/2 turn to the left.

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.

Fuel pump problems. A common malfunction that “pursues” the fuel pump is the deformation of the pump membrane. For this reason, it does not fit properly and the pump passages are not sealed..

The reasons for membrane deformation can be the following:

  • long work of the trimmer;
  • use of unsuitable fuel;
  • ingress of gases into the impulse channel.

As a result, diaphragm damage reduces pump performance and, as a result:

  • depletion of the combustible mixture occurs;
  • it is difficult to start the engine;
  • there are interruptions in the operation of the motor;
  • the piston is damaged.

Also, the above-described consequences for the engine can cause clogging of the pump cavity on the impulse side. In this case, dirt enters the membrane through the impulse channel..

To remove the blockage, you will have to disassemble the carburetor and clean the membrane..

Clogged strainer
The strainer can become dirty if contaminated fuel enters through a fuel hose or defective pickup head. In the photo below you can see what a clean filter looks like and a dirty one (parts are separated by a line).

Correcting the malfunction will require thorough cleaning and rinsing of the strainer. It is also recommended to blow compressed air through all holes in the carburetor trimmer housing..

Adjustment lever defective
This breakage occurs when the contact surface of the lever wears out..

The abrasion of the contact surface occurs due to the presence of abrasive particles in the gasoline or due to strong vibration of the engine during operation. This defect in the adjusting lever causes problems with the intake, as well as improper idling of the engine..

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Intake needle wear
The inlet needle fails, as a rule, due to the presence of abrasive particles in the fuel fluid.

  • the tightness of the inlet needle seat is disrupted;
  • there is a leakage of a combustible mixture;
  • there are malfunctions in the engine operation associated with re-enrichment of the fuel mixture.

Also, the inlet needle may just jam.

A jammed inlet needle can cause dirt in the fuel or a long idle time..

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

DIY make your own Stihl Carb Adjustment Tool in a pinch.. Lawn Care

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

Deformation of the control diaphragm
The membrane can undergo deformation during prolonged operation of the unit and when using aggressive fuels.

Failure of normal adjustment due to a defect leads to:

  • damage to the piston;
  • difficulties when starting up;
  • depletion of fuel;
  • improper engine operation.

Intake Adjustment 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..

Damper wear
The throttle and choke valves are mainly subject to wear due to the presence of abrasive particles in the air. Defective dampers look like they have been sandblasted.

As a result of valve wear, engine performance decreases, malfunctions appear in its operation, piston rings, piston and cylinder coating wear out.

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 unit.

Due to the ingress of poorly cleaned air, the shaft wears out and can 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.

How to properly adjust
Before you start adjusting the carburetor trimmer, do the following:

  • flush the engine;
  • replace or clean the spark plug;
  • change to a new one or clean the air filter (it is recommended to wash it in warm, soapy water, wring it out and let it dry well).

It is also necessary to install a cord of a suitable diameter in the trimmer coil or install knives – this is done so that during the tuning process the engine has at least some kind of load. After installing the cutting tool and starting the gasoline engine, let it warm up for 10 minutes.

If at idle speed of the engine you notice that the cutting tool rotates, then it is necessary to reduce the engine speed. This is done using the lower idle speed control, often marked with the letter “T”. But, for example, on a Stihl trimmer, this screw may be marked “LA”.

So, turn the idle speed control to the left until the trimmer head comes to a complete stop..

To adjust the carburetor, 3 regulators (screws) are used.

  • The right L regulator adjusts the enrichment level of the combustible mixture at low revs. It needs to be regulated first. Achieve maximum idle speed. This is done with the L knob by turning it left and right. After finding the point of maximum speed, return the regulator half a turn to the left (counter-clockwise).
  • The lower T (LA) adjuster is used to adjust the idle speed. Turning it to the left, the engine speed will begin to decrease, and when turning the regulator to the right, the engine speed will increase..
  • The left regulator H is responsible for enriching the fuel mixture at high speeds. The enrichment setting completes the carburetor adjustment. Also, using this regulator, you can adjust the maximum speed, fuel consumption and engine power..

Important! If the engine is allowed to run at full speed for more than 10 seconds, then it may fail..

To eliminate this nuisance, adjustment will be required. With the engine running, give full throttle, then turn the regulator “H” to the right until the speed starts to decrease. After that, the regulator “H” must be slowly scrolled to the left until you hear the uneven operation of the engine. Then you should turn the knob “H” to the right until you hear the smooth operation of the motor.

After performing the above steps, the carburetor setting can be considered complete. After correct adjustment, the engine should confidently pick up speed, a little quarter at maximum speed, and when idling, the cutting tool should not turn. This manual is suitable for adjusting carburettors on Huter, Patriot and other lawn mowers..

There are also carburetors without a screw, which is responsible for enriching the combustible mixture at low speeds. That is, they have only 2 adjusting screws: an idle speed regulator and a fuel mixture quality regulator at high speeds..

Two-Stroke Carburetor | Adjustment Screws | How they Work?

Problem 1: Clogged holes, channels and nozzles with dirt

The first thing that happens is that the holes and jets in the fuel supply system are clogged with dirt. Filters installed in the tank and directly in the carburetor do not help. They still allow small particles to pass through, which cause lawn mowers to fail..

Step 0

Install the main membrane.


Now we need to get the needle.

adjust, carburetor, stihl, lawn

To do this, unscrew the bolt on the mechanism, holding it with your finger. The fact is, there is a spring there and a careless action will lead to the fact that it will be lost..

We take out the needle, see photo and spring.


Now we remove the membrane. It is she who performs the function of pumping fuel into the carburetor..

When the membrane vibrates, the other side exerts pressure on the rocker of the mechanism and the needle rises, which, in turn, opens the hole and the fuel is supplied.

Problem 3: membrane failure

Step 3

They have the ability to wear out during operation. From prolonged use, they deform, stretch, lose elasticity, poor-quality fuel corrodes them, and can no longer perform their functions well. This also applies to the needle itself. The fact is that it is covered with a thin layer of rubber, which wears out during operation and can no longer fit tightly into the hole. the lawn mower starts to work intermittently. To eliminate such a breakdown, it is necessary to replace all worn out parts. Where to get them?

It includes two diaphragms, a gasket, a needle valve and a spring.

All wear parts of the carburetor can be replaced. Therefore, you should not rush and buy a new one, and you do not need to run to the workshop either, repairs are within the power of any lawn mower user. Professionals claim that the quality of the components in the repair kit even exceeds the characteristics of the native carburetor parts. Therefore, a well-repaired unit will perform better than a new one..


In addition, the bubble button for manual fuel pumping may fail. The impact of gasoline on it leads to the fact that during prolonged operation, the rubber corrodes and it begins to stick together or, under the influence of low temperatures, for example, during storage, it bursts. The button should also be replaced if necessary. In addition, her cost is small and will not affect the size of the repair budget in any way..

Based on the foregoing, it can be concluded that there are only three main carburetor malfunctions: clogging of channels, contamination of the fine filter and failure of components. In the first two cases, cleaning is enough, and in the third, a repair kit will help..

Principle of operation

A carburetor is a power system module in which liquid fuel and air are mixed before being fed into the engine cylinders. Mixing and flow are adjusted accordingly depending on the tool and its mode of operation..

The carburetor device for lawn mowers is the same for almost all cases. It belongs to the category of float devices. The latter provide stable parameters of ready-made mixtures.

The principle of the module is as follows.

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

The more open the air damper in the tube, the higher the density of the air flow, and, therefore, more fuel enters the cylinder. Adjusting the carburetor of lawn mowers is reduced to setting such a ratio of flaps, at which the density of the fuel mixture becomes optimal.

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Adjustment and repair of the carburetor lawn mowers

The trimmer does not belong to complex household appliances, therefore, most of its breakdowns are mechanical in nature and are quite successfully eliminated with their own hands. Even if the engine fails for serious reasons – damage to the piston ring, for example, repairs are reduced to replacing a part.

But even with a relatively simple design, such a part of the device as a carburetor needs to be adjusted..

Signs of imbalance

Debugging the carburetor is mandatory during the manufacture of the device. As a rule, the owners will find out about the need to adjust the fuel supply with their own hands only after serious enough breakdowns, in the process of correcting which, the module was removed and, for example, cleaned.

The following are the symptoms of a configuration failure:

  • starts, but the engine immediately stalls – since the engine can only work when a certain amount of gasoline is supplied, with too “lean” fuel, that is, blocking the supply channel, the engine will stop;
  • too high fuel consumption, a lot of exhaust gases – the result of incomplete combustion of the mixture. In this case, on the contrary, there is too much fuel and the mixture is too dense..

The carburetor for lawn mowers Stihl, Makita, Husqvarna and others is adjusted using the adjusting screws. Sometimes the reason for the malfunction is a violation of fixation – due to vibration or damage to the protective cap. Such a breakdown can be detected by simply trying to turn the screw slightly: if the fixation is not rigid, it is worth checking the setting.

Diy lawn mowers carburetor adjustment

Setting up the module does not apply to repair and replacement of spare parts is not required. In this case, the lawn mowers carburetor repair kit will not be needed..

Three screws are provided for debugging:

  • L – is regulated first, since it is responsible for supplying fuel at low speeds;
  • H – he is responsible for the supply of gasoline at high speeds, as well as for fuel consumption and temperature;
  • T – it is used to debug idle.

There are options, as a rule, this is the carburetor of a Chinese lawn mower, when only one screw remains on the body for debugging – for adjusting the idle speed. This does not mean that the module is configured automatically – it means that it will be difficult to carry out even such a type of repair as debugging. In the photo – adjusting the carburetor of a Chinese lawn mower.

  • The module is configured only when the engine is warm: for this, the device is pre-switched on for 10 minutes. If the mowing head rotates at idle speed, then the debugging is started immediately: turn the screw T counterclockwise until the rotation stops.
  • Adjustment begins with screw L. The screw is turned to the right and left until it is found such a position at which idle speed does not become maximum.
  • Then the screw is turned ¼ turn counterclockwise. This will be his working position..
  • Idle speed must be adjusted by turning counterclockwise to increase the number of revolutions and clockwise to decrease it. Its debugging consists in achieving such a mode in which a sufficient number of revolutions are made before the start of rotation of the mowing head. In this case, the engine must work stably at different positions.
  • The position of screw L is determined last – at maximum speed, the trimmer should not work for more than 10 seconds. The throttle opens, the screw turns clockwise, very slowly, until a decrease in the number of revolutions is audible.
  • Then, also slowly, the screw rotates counterclockwise until the motor starts to malfunction. Then the screw is turned back clockwise until the engine starts working normally again..

If there is a tanometer, and if the recommended rpm values ​​are indicated in the product passport, the correction can be made more accurate, focusing not on hearing, but on the readings of the device.

The adjustment of the carburetor of the lawn mowers in the video was carried out by ear.

8 comments on the entry “Adjustment and repair of the carburetor lawn mowers”

    Dmitry Pavlovich 07/04/2016

Please clarify. In the adjustment section p. 5, screw L – error? Should you read screw A? Thank you.

prompt the initial position of the screws H L LA


prompt the initial position of the screws H L LA

Thank you very much for the video about the accelerator and did not know, but the defect is very important and creates a huge problem that almost everyone is silent about. BRAVO….

Maybe all the same tachometer is a rpm meter, and not a tonometer blood pressure meter

and I have L, H, LA, it’s LA instead of T?

The video shows some kind of tightness, so you need to be able to chew snot.

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 indicated 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 during the preparation of the mixture the amount of oil is underestimated, after a while an extraneous sound may appear immediately after starting the engine, gradually disappearing during warming up, and the engine stops with a sharp jerk. Continued use of the trimmer in this mode will lead to its failure..

Spring may interfere

My first attempt to adjust the carburetor of the lawn mowers did not work, as the spring of the screw for adjusting the fuel mixture interfered with. The factory spring turned out to be too thick in the compressed state and did not make it possible to reduce the fuel supply to the required level. I had to pick up another spring and continue adjusting after replacing it.

Fuel mixture adjusting screw with spring

In the photo above the factory spring, below the adjusting screw with the matched spring. I am writing about this because I’m not sure if this is an isolated case, and someone else may face the same situation.

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

The purpose of the adjusting screws:

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

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

Fuel supply adjustment

Start slowly tightening 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 did not stall, 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 a quarter of a turn until the engine starts to accelerate steadily during gas blowing. 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 – counterclockwise, for some other brands the lawn mower can be the other way around.

From personal experience

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 speed to the required level using the hollow screw. Loosen the locking nut and screw in the screw to decrease the maximum speed or turn it to increase. 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 readjust the trimmer carburetor. For example, if the engine starts to rev poorly when running at full load, loosen the screw 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 capable, as stated in the instructions, to mow small shrubs up to 10 mm thick. The user’s manual is called “Petrol trimmer …”.

Idle speed adjustment

We start adjusting low speed. The screw limits the return movement of the throttle lever – by turning it, we increase the idle speed, unscrewing it, we decrease it. Adjust so that the engine runs confidently at low revs and even slightly accelerated (for better starting), but so that the line reel or knife does not rotate, and there is a sufficient reserve of revolutions before they start spinning. If the engine starts poorly, increase the idle speed even more..

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Idle speed adjustment

First of all, you need to find the position in which the idle speed will be highest by turning screw L. When you find this position using the tachometer, you need to turn the low speed screw (L) a quarter (1/4) counterclockwise … The chainsaw chain can rotate during this process. If this happens, loosen the idle screw (T) counterclockwise until the chain stops moving completely..

In what cases is it necessary to adjust the carburetor of the chainsaw?

Here is a list of the most common cases in which you need to adjust the carburetor of a chainsaw:

  • The engine starts, but the chainsaw stalls, or it cannot be started at all. Too much air in the fuel chamber may be the cause..
  • Increased fuel consumption. It can occur due to excessive saturation of the mixture that enters the engine with fuel. For the engine to work well, the mixture must be of good quality..
  • The bolts in the carburetor have lost their hold due to a damaged carburetor housing.
  • Debris entering the carburetor. This can happen if the filter is damaged or poor quality fuel is used. You will need to completely disassemble the carburetor, flush it and re-adjust.
  • Engine idling poorly or not delivering full power.

Important! If the engine is not performing well due to a worn piston, carburetor tuning will not work. In addition, along with the adjustment, it is advisable to clean the carburetor of debris – this will increase the efficiency of the procedure..

How to set the maximum speed of the chainsaw?

To change the maximum revolutions, you need to interact with screw H. If you tighten the screw, the revolutions will become higher, and if you unscrew – lower. As a rule, the highest permissible engine speed ranges from 11500-15000 per minute. If you try to work with an even higher number, the ignition problem will begin. In this case, the screw is slightly unscrewed..

How does a carburetor work?

  • When the engine is started, the air damper is opened in the carburetor..
  • The movement of the piston reduces the pressure in the air valve. This causes air to flow into the diffuser. The exact amount depends on the position of the air damper..
  • Fuel enters the float chamber. The jets regulate the speed at which this happens..
  • Gasoline and air mix with each other in the diffuser to form a fuel-air mixture. She goes to the cylinder. The mixture can be lean (a lot of air, little gasoline) or rich (little air, a lot of gasoline). The amount of the mixture entering the engine is directly proportional to its power and speed..

All processes occurring in the engine are not cyclical, but a constant basis..

How to properly adjust the chainsaw carburetor

The vast majority of gasoline saw carburetor models have three adjustment screws:

  • idle speed (T);
  • low speed (L);
  • high speed (N).

The required parameters are set by rotating these screws..

Use an electronic tachometer to fine tune the carburetor. It will make it easy to determine the engine speed of the chainsaw.

Acceleration check

If you press the gas button of the chainsaw, the engine should increase the number of revolutions. This should happen quickly enough. If the tool is gaining speed slowly, loosen the screw L a little, no more than 1/8 of a turn..

When the adjustment is completed, you need to re-check the operation of the chainsaw at idle – the engine should work properly, and the chain should remain stationary. If the engine runs unstable or the chain moves, you need to repeat the adjustment, omitting the basic setting step..

Carburetor device

A carburetor is a mechanism that is responsible for preparing a mixture of fuel and air, which is then fed into the engine cylinder. Most chainsaws have very similar carburetors, so they are set up in the same way..

The main structural details of the chainsaw carburetor:

  • Aluminium case. Aluminum is chosen as a material for its low weight. Chainsaws are a tool that must always be held in hand and carried, therefore, reducing the weight of the tool is a very important task facing the manufacturer..
  • Diffuser and choke, which are located at the inlet of the carburetor.
  • Jets – valves that provide the dosage of fuel that is supplied to the carburetor.
  • Sprayer, which is responsible for injecting fuel into the chamber.
  • Fuel chamber.

Chainsaw carburetor adjustment

Chainsaws are a very popular gardening tool. They have gained great popularity among gardeners and those who care for the territory in the local area. Chainsaws are not complete without construction or repairs. Chainsaws are even more important in the lumberjack profession..

Any chainsaw requires proper care, maintenance and adjustment before operation. Overloading the tool can shorten its life and damage the tool..

Today we will talk about that part of the chainsaw mechanism, the task of which is to prepare the fuel before it is fed into the engine cylinder. This function is performed by the chainsaw carburetor. It will depend on him how well the chainsaw works and how much fuel it spends during operation. If you see that the petrol chain saw is not working properly, the carburetor may need to be adjusted..

DIY trimmer adjustment.

High RPM Fuel Trim – H.

The third stage, correction of the amount of fuel supply at high rpm – H. For Stihl trimmers, unscrew the screw counterclockwise as far as it will go, then turn it a quarter clockwise. In general, trim adjustments from other manufacturers are almost the same. The screw is unscrewed completely counterclockwise, then the lawn mower starts and full throttle is squeezed out. Then turning the screw clockwise (usually 1/4, 2/4 turn) will decrease the maximum speed by about 5-10%. This completes the adjustment of the lawn mower. When adjusting the carburetor with this screw, turning clockwise, you reduce the fuel supply, while turning it counterclockwise, you increase.

Adjusting H trimmer

Idle speed adjustment with screw LA (T).

The second stage of adjustment is the correction of the idle speed with the LA (T) screw, here the installation is carried out exclusively by ear. Turning the screw clockwise, you increase the speed, turning it counterclockwise, you decrease the speed. It is important to ensure that the mower’s head does not spin when idling. It should also be noted that the L and LA screws are adjusted in pairs, that is, changing the adjustments on one screw may require changing the adjustments on the second. After you have achieved smooth operation of the engine with a minimum of vibrations, go to adjustment H.

Adjusting the amount of fuel delivery at low rpm L.

First of all, the upper right screw L is adjusted, that is, the amount of fuel supply at low rpm is adjusted. For Stihl fs series trimmers, screw L is turned clockwise all the way, then returned one full turn counterclockwise. This adjustment is relevant for many other trimmers. If you go from private to general, then you should achieve stable idle speed when turning the screw L, that is, the lawn mower should work smoothly and without unnecessary vibrations, as soon as you have done this go to the screw LA (T). It should also be noted that by turning the screw counterclockwise, you add fuel to the mixture, while rotating it clockwise, you reduce the amount of fuel in the mixture;

Adjusting the carburetor trimmer.

The trimmer (lawn mowers) should be adjusted according to the technical data sheet. It would be most correct to read the information in the instructions for your trimmer. It usually describes in detail how to adjust the lawn mower. If you do not have instructions for the trimmer, then you can use our advice.

Steps for adjusting the carburetor for lawn mowers:

  • Correction of the amount of fuel supply at low rpm L;
  • correction of idle speed with screw LA (T);
  • high speed fuel adjustment – H.

Trimmer adjusting screws.

Regardless of the trimmer manufacturer, each trim has three adjusting screws (very rarely two) that adjust the carburetor’s performance. Let’s take a look at the types of adjustments using the example of the professional hedgecutter Stihl fs 450.

Trimmer adjusting screws

This trimmer has three adjusting screws:

  • Top left screw (H), – adjusts the amount of fuel supply at high rpm;
  • The upper right screw (L), – adjusts the amount of fuel supply at low rpm (idle);
  • Bottom left screw (LA), – corrects the amount of idle, this screw can also be designated with the letter T;

Trimmer adjustment. Service. Introduction.

The mowing trimmer needs maintenance over the course of its life. It is important to monitor the condition of the air filter, fuel filter, and spark plug. However, even with conscientious use of lawn mowers, problems can arise. One of the possible problems can be misalignment of the trimmer carburetor. Typically, this problem arises from vibration or foreign interference in the adjusting screws of the lawn mower. Today in the article we will analyze how the trimmer is adjusted correctly and what are the main points to pay attention to..

Trimmer Maintenance