How to adjust the carburetor on a trimmer

When an adjustment is necessary

Carburetor adjustment is necessary in the following cases:

  • the new engine was run-in (4-5 liters of fuel mixture were used);
  • the fuel composition has changed (oil and gasoline brand);
  • the weather has changed (hot, cold);
  • the air rarefaction has changed (concerns mountainous areas);
  • after long storage;
  • the load on the engine has increased (after changing tools, etc.).д.);
  • due to vibration the adjustment screws unintentionally unscrewed;
  • fuel consumption has increased, the carburetor overflows fuel;
  • a spark plug electrodes are quickly fouled (the fuel mixture is prepared correctly);
  • the engine starts and immediately stops or picks up speed badly;
  • no gasoline is flowing into the cylinder;
  • large amount of exhaust gases.

When you need to adjust the carburetor of a household trimmer for grass?

Adjust the built-in grass trimmer carburetor should be adjusted when:

  • Running-in of a new engine, during which 4 to 5 liters of fuel mixture were used;
  • sudden changes in the weather;
  • Changes in air vacuum. for example, when the lawnmower is often used in mountainous terrain;
  • prolonged idling of the grass trimmer;
  • intensive increase in the load on the brushcutter’s power unit;
  • arbitrary twisting of the carburetor built-in adjusting screws. it becomes the cause of increased vibration of the engine;
  • Changes in the quality of the fuel mixture components;
  • overfilling of fuel by the carburetor, the consequence of which is an increase in fuel consumption;
  • regular appearance of a thick layer of tarry deposits and carbon deposits on the electrode surface of the standard spark plug of the grass trimmer;
  • starting the engine and its random shutdown or slow acceleration;
  • The absence of fuel flow into the cylinder of the power unit;
  • increase in the volume of exhaust gases emitted.

Lack of timely adjustment of carburetor threatens a serious breakdown trimmer for grass, up to the complete failure of his factory engine.

Carburetor for grass trimmer. How to properly adjust the grass trimmer carburetor.

On trimmers, in addition to electric motors, gasoline internal combustion engines are installed. This mechanism requires special attention to itself, because if not properly adjusted, it will either refuse to work, or will work with interruptions and loss of power. Basically, the adjustment of the engine is to adjust the fuel supply, and this is done with the grass trimmer carburetor.

The regular design of any gasoline trimmer for grass necessarily includes a fuel system, the basis of which is the action of the regular carburetor. Its design and initial principle of operation are virtually the same for all brushcutters, regardless of their design and purpose.

The brushcutter carburetor consists of an all-metal aluminum housing that protects the internal components of the assembly from moisture, small debris and dust. The underside of the housing has an integral diffuser, also known as a Venturi nozzle. The primary function of this part is to supply the amount of air required by the fuel system to enrich the fuel. The diffuser works on a simple principle: the smaller its diameter becomes, the more air is drawn in. This is due to the fact that in the area of the smallest diameter the level of air rarefaction becomes maximum.

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

The carburetor on a brushcutter has a throttle valve whose main task is to adjust the intake air volume. The greater the amount of air, the higher the power rating of the weed trimmer. Another function of the choke is to make it easier to start the engine when it is cold. If the lawnmower is being started for the first time after a long standstill, the choke must be closed. Immediately after starting the engine, the part must be opened, otherwise the engine will stall.

Carburetor for grass trimmer is equipped with a pulse channel, which connects the inner cavity of the crankcase with the impulse chamber of the pump. The piston located in the engine cylinder creates reciprocating movements that cause the pressure inside the crankcase to change in stages. At the same time the diaphragm is actuated. Thus, the pump action is fully synchronized with the work of the power unit.

How To Adjust a Trimmer Carburetor, Poulan Pro, Craftsman, Weed Eater, Zama, 2-Stroke Carburetor

The diaphragm of the standard carburettor actively takes part in the fuel intake. It enters the fuel assembly through the. Fuel then passes through the inlet and outlet valves, then through a strainer and fuel pipe. Fuel then flows near the needle and gradually fills the chamber equipped with a control diaphragm.

The standard grass trimmer carburetor valve is connected to the diaphragm by a lever. Below the built-in diaphragm is a cavity into which air is sucked through a special hole.

The carburetor for a lawn mower works on this principle in stages. This ensures uninterrupted operation of the fuel assembly and a smooth supply of fuel to the cylinder of the original power unit.

When you need to adjust the carburetor of a domestic grass trimmer? Adjust the grass trimmer’s built-in carburetor at:

  • running-in of the new engine, during which 4 to 5 liters of fuel mixture were used;
  • sudden changes in the weather;
  • Changes in air flow such as when the lawnmower is frequently used in mountainous terrain;
  • Continuous downtime of the grass trimmer;
  • The carburetor of a brushcutter includes a throttle, whose main task is to adjust the volume of the intake air;
  • arbitrary unscrewing of the carburetor’s built-in adjusting screws, which causes increased vibration of the engine;
  • changes in the quality of the fuel mixture components;
  • Fuel overflow from the carburetor, resulting in increased fuel consumption;
  • regular occurrence of thick layer of tarry sediments and carbon deposits on the surface of electrodes of standard spark plugs of grass trimmer;
  • start of the engine and its random shutdown or slow acceleration;
  • lack of fuel supply to the power unit cylinder;
  • increase in the volume of exhaust gases emitted.

Lack of timely adjustment of carburetor threatens a serious breakdown of grass trimmer up to complete failure of its original engine.

Adjusting the lawn mower carburetor with your own hands. Periodic adjustment of the grass trimmer carburetor should be done on a serviced and fully functional power tool. Before starting the procedure, the operator must thoroughly wash the parts of the engine and inspect its CPG for burrs or other defects. In addition, it will be necessary to clean or change the spark plug, as well as wash the filter elements in the construction of the brushcutter.

During the adjustment of the carburetor, the engine of the lawnmower must work under a certain load. It is best to install a proper diameter cord or cutting blades on the grass trimmer.

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After installing the cutting attachments, the operator must start the engine of the grass trimmer and leave it running for about 10 minutes. If while the power unit is running at idle speed it has been noticed that the cord or blade is rotating, then it is necessary to reduce the speed generated by the motor. To do this, turn the lower regulator, often designated by the letter T, to the left side, until the set cutting unit comes to a complete stop. Further scheme of fuel assembly adjustment is as follows:

  • The L knob on the right is used to mix fuel with air when the engine reaches a low RPM. The position of this screw must be adjusted first. To do this the operator needs to achieve maximum engine rpm when idling for this turn the L screw to the right or left side in turn. Once the maximum rpm has been reached turn the screw 1/2 turn to the left;
  • Screw T or LA is necessary to adjust the idle speed. When you turn it to the left, the engine speed will decrease, and when you turn it to the right, respectively, will increase;
  • Regulator H on the left is responsible for enriching the fuel mixture with air when the engine of the grass trimmer works at high rpm. This screw is also needed to adjust the power of the engine and the amount of fuel used. Adjustment of its position is done by turning the screw to the right or to the left side until the maximum permissible engine rpm is reached. After that it is necessary to turn the H screw 1/2 turn to the left.

Common carburetor malfunctions. Grass trimmer carburetor failures occur due to the use of low-quality gasoline, a damaged air filter, and dirt accumulation in the chamber of this unit. Most often, the repair of the carburetor with their own hands is quite possible. The following are typical problems with the brushcutter carburetor.

The problems of the fuel pump. A common problem that haunts a fuel pump is a deformed pump diaphragm. It does not fit properly and the pump passages are not sealed.

The causes of deformation of the diaphragm may be as follows:

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

  • there is a depletion of the combustible mixture;
  • Difficulty in starting the engine;
  • the motor ceases to function correctly;
  • the piston is damaged.

Also the above consequences to the engine can be caused by clogging of the pump cavity on the impulse side. In this case, dirt will enter the diaphragm through the impulse channel.

In order to remove the dirt, the carburettor must be disassembled and the diaphragm cleaned.

Plugged strainerThe strainer can become dirty if contaminated fuel enters through the fuel hose or a defective suction head. In the photo below you can see how a clean and dirty filter looks like (parts are separated by a line).

Corrective action will require thorough cleaning and flushing of strainer. It is also recommended to blow with compressed air all the holes in the carburetor body of the grass trimmer.

Adjustment lever faultyThis fault occurs when the contact surface of the lever wears out.

Wiping of the contact surface is caused by abrasive particles in the petrol or by strong vibrations of the engine during operation. This defect in the adjusting lever causes intake problems as well as misfiring of the motor at idle speed.

Inlet needle wearThe inlet needle fails, usually due to abrasive particles in the fuel fluid.

  • sealing of the inlet needle seat becomes compromised;
  • there is a leakage of fuel mixture;
  • malfunctions occur in the engine due to over-enrichment of the fuel mixture.

It is also possible for the inlet needle to get stuck.

Inlet needle jamming can be caused by dirt in the fuel or by the machine sitting idle for long periods of time.

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

It causes fuel over-enrichment and the engine does not run properly. The carburetor needs to be disassembled and the diaphragm chamber needs to be cleaned.

Deformation of the regulating diaphragmThe diaphragm may be permanently deformed in continuous machine operation or if aggressive fuels are used.

Failure of normal adjustment due to a defect leads to:

Throttle valve problemThrottle valve problem can occur if throttle valve lever is installed incorrectly or if you bend it before installing it. As a result, the contact surface takes the wrong position, which disturbs the additional fuel supply.

adjust, carburetor, trimmer

Wear at the throttle and air valves is mainly caused by abrasive particles in the air. Defective flaps look like they have been sandblasted.

Damper wear results in reduced engine performance, malfunctions, piston rings, piston and cylinder liner wear.


Throttle and air damper shaft wearThe throttle and air damper 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.

The filter should be washed in soapy water and dried. Broken shaft pieces can enter the combustion chamber or engine crankcase and cause serious damage to the entire piston system.

To eliminate air cleaning problems, you must replace the defective filter or wash the existing (serviceable). The filter should be washed in soapy water and dried.

How to properly make adjustmentsBefore you start adjusting the grass trimmer carburetor, you need to do the following:

  • flush the engine;
  • replace or clean the spark plug;
  • Change or clean the air filter (it is recommended to wash it in warm, soapy water, squeeze it and let it dry well).

It is also necessary to install a cord of suitable diameter in a trimmer reel or to install knives, this is done so that in the process of adjustment the engine had at least some load. After installing the cutting tool and starting the gasoline engine, let it warm up for 10 min.

adjust, carburetor, trimmer

If you notice that the cutting attachment is rotating when the engine is idling, you need to reduce the engine speed. This is done with the lower idle speed regulator, often marked with “Т”. But on a STIHL trimmer, for example, this screw may be marked “LA”.

Now turn the idle speed controller to the left until the trimmer head comes to a complete stop.

There are 3 adjusters (screws) used for carburetor adjustment.

  • The right regulator L adjusts the level of fuel mixture enrichment at low RPM. This needs to be adjusted first. Reach maximum idle speed. This is done with the L Controller by turning it to the left and right. After reaching the maximum RPM point turn the regulator half a turn to the left (counterclockwise). arrow).
  • The lower regulator T (LA) is used for adjusting the idle speed. Turning it to the left will begin to decrease engine RPM, and turning the regulator to the right will increase RPM.
  • The left hand exhaust valve H controls the fuel-enrichment process at high rpm. The enrichment setting completes the carburetor adjustment. The maximum RPM, fuel consumption and engine power can also be adjusted with the Enrichment adjustment knob.
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Important! If allowed to run at full rpm for more than 10 seconds it may go.

To avoid this mishap, adjustment is necessary. With the engine running give full throttle and then turn the regulator “H” to the right until the rpm starts to drop. After that the regulator “H” you need to scroll slowly to the left until you hear an uneven engine. Turn the control knob “H” to the right until the engine is running smoothly.

After performing the above steps, carburetor adjustment can be considered complete. After the correct adjustment, the engine should be able to rev steadily gain RPM, should quadruple at maximum RPM, and should not rotate when idling. This guide is suitable for adjusting carburetors on Huter, Patriot and other chain saws.

there are also carburetors without a screw that enriches the fuel mixture at low rpm. That is, they have only 2 adjusting screws: the idle speed regulator and the fuel mixture quality regulator at high rpm.

When the carburetor needs to be adjusted?

Stable operation of a brushcutter carburetor depends to a large extent on its proper adjustment.

Adjustment of the unit is required in the following cases:

  • After running in a new grass trimmer, when during the work 4-5 full tanks of fuel have been used;
  • when the operator frequently changes the brand of gasoline used for refueling;
  • as a result of a sudden change in the weather;
  • Due to the long storage time of the grass trimmer;
  • As a result of arbitrary unscrewing of adjusting screws of a brushcutter, caused by strong vibration of its engine;
  • due to a sharp increase in the amount of fuel consumed by the trimmer.

You will also need to adjust the carburetor on your brushcutter if the tool’s spark plug quickly becomes soiled or if the volume of exhaust gases from the trimmer suddenly increases.

Lawn mower carburetor adjustment and repair

trimmer for grass to the complex household appliances do not apply, so most of his failures are of a mechanical nature and rather successfully eliminated with their own hands. Even if the engine fails for serious reasons. damage to a piston ring, for example. repairs are limited to replacing the part.

Correct Way To Adjust Or Tune The Carburetor On A Weedeater / Grass Trimmer

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

Adjusting the carburetor of a lawn mower from a German manufacturer

The use of a lawnmower in works with landscaping involves wear and tear, and sometimes breakdowns of its mechanisms. But since this tool can not be attributed to complex household appliances, all the failures are purely mechanical, which can be corrected with your own hands. In some cases, it is enough to carry out adjustment work, returning the tool to normal working condition. One such operation is the adjustment of the lawnmower carburetor in manual mode. The task of the carburetor is to mix air with fuel before feeding it into the engine. And if the proportions do not match, there will be visible failures in the work of the grass trimmer:

The whole process of adjusting the carburetor of a brushcutter brand involves only debugging the position of three screws: L. adjustment of gasoline supply in the mower at low revolutions, H. adjustment of high revolutions and fuel consumption, T. adjustment of idle speed. So, if you need to adjust the carburetor of a gasoline lawnmower line 55 or other types of this series, the following steps are performed:

  • Warm up the engine (10 minutes idling time is enough).
  • Adjusts the H screw by turning to the left/right until the engine reaches maximum idle speed.
  • From the point found, turn counterclockwise by ¼ turn, which will set the desired operating position.
  • The adjustment of the idling speed of the gasoline mower carburettor is made similarly, turning counterclockwise (decreasing revolutions) and clockwise (increasing revolutions). The position of maximum stability of motor operation at different positions is reached.
  • Adjust the L screw in the same way, turning it a little to the maximum setting.

The whole process is performed by ear, so for a more successful work it is worth to get a tanometer. Maximum precision maintenance of the tool is available from the masters “Grasshopper Motors”, as well as buy oil for the compressor and buy all the necessary spare parts and components for timely maintenance.

Flush the air filter before adjusting the carburetor. We recommend flushing it after every 10 hours of operation. After that, you may adjust the carburetor. The picture shows the carburetor of the PRORAB-8406 gasoline grass trimmer for example. The numbers indicate the adjusting screws we will use.

PRORAB-8406 Gasoline grass trimmer carburetor adjustment screws

Start the lawnmower and wait for it to warm up.

Adjusting the fuel flow

Start turning the fuel mixture adjustment screw slowly until the engine starts to stall or stalls if you don’t have time to catch it. After that, turn the screw a quarter-turn if the engine has not stalled, or a half-turn if it has stalled. Start the stalled engine. Check how the engine picks up speed by opening the throttle. Continue loosening the screw a quarter turn at a time until the engine starts to steadily pick up higher revolutions when cranking. This will be the point at which the engine is most economically stable. For gasoline grass trimmer PRORAB-8406 adjusting screws are screwed clockwise, unscrewed. counterclockwise, with some other brands of chain saw can be the opposite.

Idle speed adjustment

Now we adjust low revolutions. The screw limits return motion of throttle lever. by screwing it in, we increase idle speed, by unscrewing it we decrease idle speed. Adjust so that the engine works confidently at low RPM and even a little faster (for a better start), but that the spool with a fishing line or a knife do not rotate, and before the start of their rotation there is enough margin. If the engine starts poorly, increase the idle speed even further.

Maximum rpm limitation

after adjusting the fuel mixture and low revolutions, check how the lawnmower engine will run at maximum rpm. If necessary, limit maximum rpm to desired level with hollow screw Loosen retaining nut and screw in to reduce maximum rpm or unscrew to increase. After adjusting, tighten the nut. Setting the maximum speed needed to protect the grass trimmer engine from overheating and the ability to use the starter button lock to reduce right hand fatigue.

You may need to adjust the grass trimmer carburetor later on. For example, if the engine starts to stall under full load, back off the screw a quarter turn more. Increase idle speed if it is difficult to start. The operation of the lawn trimmer can also be affected by weather conditions and the quality of the fuel mixture. Vibration can cause the adjusting screws themselves to turn.

Grass trimmer adjustment. How to Adjust the Carburetor?

The grass trimmer for mowing grass needs maintenance during its lifetime. It is important to check the condition of the air filter, fuel filter and spark plug. But even with good use of the lawnmower, problems can occur. In particular, one of the possible problems can be a carburetor adjustment grass trimmer. The problem is usually caused by vibration or tampering with the adjusting screws on the brushcutter. Today in the article we will consider how the grass trimmer is properly adjusted and what the main points you should pay attention to.

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Adjustment screw.

As you know, regardless of the manufacturer of the grass trimmer, every trimmer has three adjusting screws (very rarely two), which regulate the operation of the carburetor. Let’s review the types of adjustments on the example of a professional hedge trimmer STIHL fs 450.

So, there are three adjustment screws on this trimmer:

  • The upper left screw (H), adjusts the fuel rate at high rpm;
  • The upper right screw (L), adjusts the amount of fuel supply at low rpm (idle);
  • The lower left screw (LA), adjusts the idle speed, this screw can also be marked with the letter T;

Grass trimmer carburetor adjustment.

As a rule of thumb, the grass trimmer (lawnmower) should be adjusted according to the datasheet. It is particularly worthwhile reading the information in your trimmer’s manual. It usually has detailed information on how to adjust the trimmer. If you do not have a trimmer manual, you can use our tips.

Steps for adjusting the lawn trimmer carburetor:

  • Adjustment of the fuel rate at low RPM L;
  • correction of idle stroke value with LA (T) screw;
  • Adjustment of fuel flow at high RPM H.

Fuel adjustment. Low RPM (L).

The first thing to adjust is the upper right L screw, i.e. adjusting the amount of fuel at low rpm. For STIHL fs series trimmers, turn the L screw all the way clockwise, then return one full turn counterclockwise. Besides, such adjustment is also relevant to many other trimmers. If you want to make a generalisation, you have to achieve a stable idle speed with the screw L, i.e. the mower has to run smoothly and without any vibrations, once you have done this, go to the LA (T) screw. It should also be noted that turning the screw counterclockwise adds fuel to the mixture, turning it clockwise reduces the amount of fuel in the mixture;

adjustment of idle speed.

The second stage of adjustment, is the adjustment of the value of the idle stroke with the screw LA (T), here the setting is made only by ear. By turning the screw clockwise you increase rpm, by turning it counterclockwise you decrease rpm. It is important to make sure that the mower head does not spin idle. it is also worth noting that the L and LA screws are adjusted in pairs, i.e. changing the settings on one screw may require changing the settings on the other. Once you have achieved a smooth operation of the engine with a minimum of vibration, proceed to the adjustment H.

Adjusting the fuel flow. High revolutions (H).

Third step, adjusting fuel rate at higher RPMs H. For STIHL trimmers, turn the screw fully anticlockwise, then turn a quarter turn clockwise. In general, the adjustment of trimmers from other manufacturers is almost the same. Turn the screw fully anticlockwise as a rule, start the lawnmower and throttle up to full throttle. Then turn the screw clockwise (usually 1/4, 2/4 turn) to reduce the maximum rpm by about 5-10%. The adjustment of the lawnmower is now complete. When adjusting the carburetor with this screw, turning clockwise reduces the fuel supply, turning counterclockwise increases the.

Grass trimmer adjustment. Conclusion.

It should be remembered, the correct adjustment of the grass trimmer not only allows you to increase the service life, but also allows you to save fuel. It is important to make sure the grass trimmer is working correctly. The lawnmower must run smoothly, without excessive perceptible vibrations and pick up speeds evenly. In this case, in idle mode, the grass trimmer head should not rotate.

Before any adjustment of the grass trimmer, first check the condition of the filters: fuel and air filter, as well as the spark plug. The problem may lie in these elements. The fuel filter should be easy to blow and not visibly dirty. The candle should be clean, dry and slightly brownish. If the spark plug is wet and has a black tint, it means that it is flooded and it is necessary to reduce the fuel supply by adjusting screws. A whitish tint on the spark plug indicates that the mixture is depleted on the contrary, you need to add fuel supply.

adjust, carburetor, trimmer

If all the elements are in order and adjustments are not yielding the desired results, it may be time to clean the carburetor. How to clean the carburetor of a gasoline-powered machine, we will explain in one of our next articles.

How the lawnmower carburetor works

The throttle valve determines the amount of air to feed, and this directly affects the power of the engine.

Fuel is sucked into the carburettor system by a pump (its diaphragm). Then passes through the nozzle in the carburetor. Then the fluid moves through the intake and exhaust valves of the pump. Is filtered by the grid. The needle valve moves into the diaphragm chamber.

  • Air supply to the tube with an air baffle (damper). Baffle plate controls the intensity of the air flow.
  • The fuel system is necessarily narrowed by a diffuser to increase the rate of flow.
  • Gasoline through the float chamber and nozzle tube with constriction. The float chamber controls the temporary volume of gasoline. The float chamber has a neutral pressure level, but the tube with constriction is already low. Differential pressure causes the fuel to flow through the nozzle.
  • Acceleration of the air flow promotes the fuel (gasoline) transfer and atomization. The result is an air-fuel mixture of the desired proportion or density.
  • The air-fuel mixture enters the engine cylinder through the fuel tube.

The area of the open air damper affects the level of air density in the system. The wider the flap is open, the higher the fuel consumption and power.

Simply put, adjusting the carburetor on a chainsaw is to create an optimal fuel mixture by correcting the air supply.

Design and adjustment of the carburetor on chain saws and trimmers

lawnmower or grass trimmer with an internal combustion engine requires not only constant refilling of the fuel mixture of gasoline and oil, but also periodic adjustment of this fuel. For the supply of fuel into the cylinder of the lawnmower is responsible for the carburetor, the efficiency and performance of the tool depends on the proper operation. If a faulty (abnormal) engine operation is detected during operation, the first thing to do is to adjust the lawnmower carburetor. Before adjusting the carburetor of a gasoline trimmer for grass, let’s first understand its construction.

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