How to put a carburetor on a grass trimmer

How to properly adjust the carburetor trimmer for grass

On trimmers, in addition to electric motors, gasoline internal combustion engines are installed. This mechanism requires special attention, 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.

It is almost unrealistic to cover all the varieties of carburetors, produced by manufacturers of gasoline trimmers. But, since the design of this module, as well as its principle of operation is largely similar between different models, we can make a generalized description of the processes that occur in the carburetor. This information will allow the user to understand the principles of operation of the unit, to correct malfunctions and to operate it correctly.

The grass trimmer’s carburetor is based on a solid piece of aluminum. Below is a schematic diagram of this unit.

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

The smaller this opening, the faster the air flows and the higher the level of negative pressure in the area with the smallest diameter.

At the top of the diffuser are the fuel passages (11,12). The air flow through these channels draws in gasoline. The fuel pump itself, the nozzles and the system used to adjust the fuel-air mixture can be built-in or externally installed.

The throttle valve (9) controls the amount of air drawn into the carburettor. Its quantity affects the power, which the engine develops. The slide valve (7) serves for cold start. It must be closed if you are going to start the machine. Open the fuel filler cap after starting the engine, otherwise the engine will stop immediately.

The impulse port (1) connects the impulse chamber of the pump with the engine crankcase, namely with its internal volume. The piston, which is in the cylinder, making reciprocating movements, consistently changes the pressure in the crankcase (vacuum or pressure increase). The differential pressure forces the diaphragm (4) to move. Therefore, the work of the pump is synchronized with the work of the motor.

It is the diaphragm that draws gasoline from the tank (4). Petrol enters the carburettor through the nozzle (2). Then, its path goes through the inlet valve (3), the outlet valve (5), through the strainer (6), the fuel channel (10), past the needle (14) and fills the chamber (16) that has the control diaphragm (18).

The valve (14) through the lever (17) connects to a diaphragm (18). The cavity below the diaphragm communicates with the ambient air through the hole (19).

The device works in the following way.

  • During the suction stroke a vacuum is created in the diffuser. This fact causes air suction. The position of the throttle valve (9) determines the amount of air entering the carburettor chamber, as well as the engine power and the number of its revolutions.
  • At this time through the nozzles (11,12) fuel is sucked from the chamber (16), then it is mixed with the flowing air. Gasoline mixes with the air and starts to atomize. This creates an air-fuel mixture.
  • The ready mixture enters the cylinder, where it is compressed by the rising piston and ignited at its highest point by a spark produced by the spark plug.
  • As the volume under the control diaphragm (18) is connected to the atmospheric air through a channel (19), the diaphragm moves upwards, opening the valve (14) with the lever (17). After the valve (14) is opened, a new portion of fuel enters the chamber (16).
  • Once the chamber (16) is filled, the diaphragm (18) returns to its original position and the valve (14) closes.

Further, when the engine is running, all the above-described processes are repeated. To adjust the amount of fuel entering the diffuser through the nozzles, screw (13). To adjust the idle speed the screw (15) is also used. Cranking out the regulators makes the fuel mixture richer, and tightening the regulators makes the mixture leaner. Also in some models of carburetors it is possible to adjust the idle speed of the engine with a quantity regulator. the regulator is normally located on the outside of the throttle, and when it is tightened, the lever rests on the axle of the throttle.

In this way, using the 3 adjusting screws, you can achieve maximum motor performance, and set it to run smoothly at any ambient temperature, and even in mountainous areas.

Grass trimmer carburetor. How to properly adjust the grass trimmer carburetor.

In addition to electric motors, trimmers are equipped with gasoline internal combustion engines. 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 trimmer carburetor for grass.

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In 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 features 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. In the lower part of the body there is a built-in diffuser, the second name of which is the “Venturi nozzle.

The main function of this OEM part is to supply the air in the amount required by the fuel assembly to enrich the fuel. The diffuser works according to a simple principle: the smaller its diameter becomes, the more intensive the air intake. This is because in the area with the smallest diameter the level of air rarefaction is greatest.

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. The other carburetor parts: the regular adjusting screws and the fuel pump. may be located both inside and outside of the carburetor.

The design of the brushcutter carburetor includes a throttle valve, whose main task is to regulate the volume of intake air. The greater the amount of air, the higher the power rating of the grass trimmer power unit. Another function of the flap is to make it easier to start the engine cold.

The carburetor for grass trimmer is equipped with a pulse channel that connects the inner cavity of the crankcase with the pulse chamber of the pump. The piston, located in the engine cylinder, reciprocates and causes a step change in pressure inside the crankcase.

The diaphragm of the standard carburetor takes an active part in fuel suction. It enters the fuel assembly through a nozzle. The fuel then flows through the inlet and outlet valves, then through the strainer and through the fuel pipe. Fuel then flows near the needle and gradually fills the chamber equipped with a control diaphragm.

carburetor, grass, trimmer

The grass trimmer carburetor‘s OEM 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 lawnmower 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 the carburetor of a domestic grass trimmer needs adjusting? 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;
  • variations in air pressure. e.g., when the lawnmower is frequently used in mountainous terrain;
  • prolonged downtime of the grass trimmer;
  • Intensive increase in the load on the brushcutter’s power unit;
  • arbitrary unscrewing of the built-in carburetor adjusting screws. this causes increased vibration of the engine;
  • change of quality of the fuel mixture components;
  • Overcharging the carburetor, resulting in increased fuel consumption;
  • the regular appearance of a thick layer of tar deposits and carbon deposits on the surface of the electrodes of the standard spark plug of the grass trimmer;
  • engine starting and its random shutdown or slow acceleration;
  • Lack of fuel flow into the cylinder of the power unit;
  • increase in the volume of emitted exhaust gases.

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

Lawn trimmer carburetor adjustment with your own hands. Periodic adjustment of the grass trimmer carburetor must be performed on a serviced and fully serviceable power tool. Before starting the procedure, the operator must thoroughly wash parts of the engine and inspect its CPG for burrs or other defects.

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

After installing the cutting tools, the operator should start the grass trimmer‘s engine and leave it running for about 10 minutes. If during work of the power unit at idle rpm it is noticed that the cord or knife rotates, then it is necessary to reduce the engine rpm.

  • Regulator “L”, located on the right side, is responsible for enrichment of fuel mixture with air during engine operation at low revolutions. This should be the first screw to be adjusted. To do this you need to get the maximum RPM of the engine when idling. to do this turn the “L” screw to the right or left side alternately. Once maximum RPM is reached it will be necessary to turn the screw 1/2 turn to the left;
  • screw “T” or “LA” is needed to adjust the idle speed. When turning it to the left the engine RPM will decrease, and when turning it to the right. respectively, will increase;
  • The regulator “H”, provided on the left, is responsible for enriching the fuel mixture with air when the engine of the grass trimmer works at high revolutions. This screw is also needed to adjust the power of the motor 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 “H” screw must be turned 1/2 turn to the left.

Construction of a gasoline carburetor and its purpose

lawnmowers are equipped with a two-stroke internal combustion engine. To supply air-fuel mixture to the engine cylinder, the carburetor is used. In the construction of gasoline units. it is a key element, without which the work of the engine is impossible. And this carburetor differs from the car device not only in size, but also in the principle of operation.

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Structurally, the entire mechanism is a small piece with channels, valves, and diaphragms inside. The carburetor body is made of aluminum and the internal arrangement is shown in the photo below.

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Before the adjustment of the lawn mower carburetor with your own hands, it is necessary to understand all the constituent elements of the device in question. The lawnmower and grass trimmer carburetor consists of the following parts:

  • Diffuser or Venturi nozzle. the air is sucked into the system through this nozzle
  • Air valve. opens and closes the filtered air supply
  • Fuel channel of maximum revolutions
  • Fuel pipes (nozzles) of idling and medium speed
  • Throttle valve. the amount of opening is regulated by pressing the throttle
  • Pulse duct connector. connects to the inner crankcase channel of the engine
  • Fuel inlet channel (nozzle) (2). provides fuel supply from petrol tank
  • Diaphragm (4). is responsible for sucking fuel from gas tank
  • Fuel suction valve from the tank (3)
  • Fuel valve to carburetor channel (5)
  • Fuel filter element (6) or fine filter
  • Fuel line (10)
  • Needle of the needle valve (14). is responsible for supplying fuel into the control diaphragm chamber
  • Chamber. fuel mixture that is fed through nozzles and throttle valve into the cylinder
  • Control diaphragm (18). provides manual fuel priming
  • Lever connected to the diaphragm (17)
  • Idle speed adjustment screw (15)
  • Diffuser fuel adjustment screw (13)

If you know how the carburettor is assembled internally, it is necessary to understand the principle of its operation. A detailed description of how the carburetor on a two-stroke internal combustion engine works, using a chainsaw as an example, is described in this material.


A list of work to be done on the engine may include the following

  • Changing the fuel pump;
  • disassembly and flushing of the strainer;
  • Replace the adjustment lever;
  • You must also clean the adjustment space;
  • replacing the diaphragm (or the entire unit where the diaphragm is located);
  • Adjustment of inlet, outlet and needle valves;
  • valve replacement;
  • cleaning of fuel ducts and diffuser;
  • replacing the screw springs;
  • Changing the primer.

Not all of these jobs can be done. Often it turns out that many of them are not necessary if a specific fault is immediately detected.

Adjusting the carburetor on a chainsaw

Diagnosing and adjusting the carburetor with your own hands may only take a few minutes.

Before starting, flush the filters (see the section titled “Repairing and installing the spark plugs”). instructions). You can adjust the carburetor yourself with three adjusting screws.

To do it right, start the engine. Your steps are as follows.

carburetor, grass, trimmer
  • Find the idle speed limit. To do this, turn the L screw to the right and then to the left. Turning step. a quarter turn counterclockwise.
  • With the T screw you can adjust the idle RPM of the motor: clockwise increase with one turn of the screw, anticlockwise decrease with another. The engine is running smoothly with no load and no warm-up. When warmed up it does not increase the engine speed.
  • If you are not adjusting a brushcutter but a grass trimmer, turning the T screw sets a larger RPM margin. Both types of machines have a stable RPM when the blade (or line) selects the height of cut.
  • Turn the H screw last. This sets the rate of petrol and air at close to maximum RPM, engine power, engine temp and fuel consumption.

To adjust the motor from the H screw do the following.

  • Open the throttle and squeeze the throttle at maximum rpm.
  • Turn the H screw clockwise until the engine speed lowers.
  • Turn the same screw slowly counterclockwise until the motor spins erratically.
  • Turn the screw back a little (clockwise) until the engine is running smoothly. It’s important to get that edge.

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The result of accurate adjustment. complete combustion of fuel and a white-brownish color of the spark plug. The spark plug filled with petrol is much darker than the un-filled one.

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Common malfunctions of carburetors

Grass trimmer carburetor breakdowns occur due to the use of poor quality gasoline, a damaged air filter and dirt accumulation in the chamber of this unit. Most often, it is quite possible to repair the carburetor with their own hands. Here are some common problems with your brushcutter carburetor.

Fuel Pump Problems

A common problem that “haunts” the fuel pump is a deformation of the pump diaphragm. It does not seat properly and the pump ports do not seal properly.

Causes of deformation of the diaphragm may be as follows:

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

  • Depletion of the fuel mixture;
  • makes it difficult to start the engine;
  • engine irregularities occur;
  • The piston is damaged.
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Clogging of the pump cavity on the impulse side may also cause the above-mentioned consequences for the engine. In this case, the dirt gets on the diaphragm through the impulse channel.

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

Plugged strainer

The strainer can get dirty if contaminated fuel comes through the fuel hose or a defective suction head. The picture below shows a clean and dirty filter (the parts are separated by a line).

To fix the problem, you will need to thoroughly clean and rinse the strainer. It is also recommended to blow all the holes in the carburetor housing of the grass trimmer with compressed air.

The adjustment lever is defective

This failure occurs when the contact surface of the lever is worn.

Wiping of the contact surface occurs due to abrasive particles in the gasoline or due to strong vibration of the motor during operation. This defect in the adjusting lever causes problems with the intake, as well as improper operation of the motor at idle speed.

Worn intake needle

The inlet needle fails, as a rule, because of the presence of abrasive particles in the fuel fluid.

  • the sealing of the inlet needle seat is compromised;
  • There is a leakage of combustible mixture;
  • malfunctions appear in engine operation due to over-enrichment of the fuel mixture.

Also the inlet needle can get jammed.

Inlet needle jamming can cause dirt in the fuel or long periods of machine inactivity.

Clogged regulating cavity

If dirt accumulates in the throttle cavity, the inlet needle will not seal tightly and a lot of fuel will flow into the chamber.

This causes fuel over-enrichment and the engine does not run properly. The carburetor must be disassembled and the adjustment diaphragm cavity cleaned.

Deformation of the regulating diaphragm

Diaphragm may be distorted by prolonged unit operation and corrosive fuels.

Failure to adjust properly due to the defect results in:

Trouble with inlet adjustment lever

This problem can occur if the adjustment lever is installed incorrectly or if it is bent before installation. As a result, the contact surface is in the wrong position, which prevents additional fuel supply.

Wear on the flaps

Throttle and air dampers are mostly worn due to abrasive particles in the air. Defective flaps look like they have been sandblasted.

Throttle valve wear reduces engine performance, malfunctions, piston rings, piston and cylinder liner wear.

Throttle and air damper shaft wear

The air and throttle shaft can wear due to the following causes:

carburetor, grass, trimmer
  • Insufficient and improper maintenance of the air filter;
  • the air filter is damaged;
  • The air filter is unsuitable for this machine.

Due to improperly cleaned air, the shaft will wear out and may break. Broken off parts of the shaft can enter the combustion chamber or engine crankcase and cause serious damage to the entire piston system.

To fix problems with air purification, you need to replace the defective filter or wash the existing (serviceable). The filter should be washed in soapy water and dried.

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That’s why gas stations do not allow gasoline in plastic canisters, only in metal canisters. Before pouring gasoline in a metal canister, it is better to put it on the ground, so it removes static from the body. To develop a channel, if anyone can help with funds. I will be grateful. Privacy : 4149439315000673 Webmoney WMZ : Z610102394928.

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