How to adjust the carburetor on a STIHL trimmer

Common carburetor malfunctions

Failure of the grass trimmer carburetor is caused by the use of poor quality gasoline, a damaged air filter, and 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 brushcutter carburetor malfunctions.

Damper worn out

The throttle and air damper become unusable due to the ingress of dust, metal particles, etc. with the air flow. Damaged dampers are similar to parts that have been blasted with sand. Due to wear on the dampers, the efficiency of the motor decreases, and breakdowns are detected. Piston and cylinder wear out.

Stihl FS 94 R Line Trimmer Carburetor Adjustment

The dampers become unusable due to improper maintenance of the air filter or its breakdown.

In some cases, this filter is simply not suitable for your brushcutter or grass trimmer model. In the end, the motor shaft will suffer. its pieces fall into the engine channels, which will cause the piston to be broken.

Grass trimmer carburetor

The grass trimmer carburetor is one of the most important parts of the machine, which is responsible for the fuel mixture. If the equipment is handled incorrectly, the element may be damaged, which makes it impossible to operate the brushcutter without repair. To repair a garden tool, you need to know about its structure, the principle of functioning and the rules of adjustment.

Design features and operating principle of the lawn mower carburetor

Structurally, carburetors practically do not differ from well-known brands and Chinese manufacturers.

The carburetor device of the brushcutter consists of the following elements:

  • Booster pump;
  • Tuning systems with atmospheric membrane;
  • A primer that makes it easier to start the motor;
  • Cold running systems;
  • Elastic two-valve plate;
  • Dosing system with a rotating rotor;
  • Throttle.

The model functions as follows:

  • From the air damper, air passes into a tube, which increases or decreases its flow;
  • In the area with a hole for the fuel mixture, the narrowed zone is a diffuser. In this zone, the air moves faster;
  • The fuel mixture from the float chamber enters the pipe through the nozzle. The amount of fuel is determined by the float;
  • The increased air flow picks up the fuel and disperses it. An air-fuel mixture with sufficient density is created;
  • Sucks the mixture with a cylinder through the pipeline.
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The concentration of the air flow depends on how slightly open the aerosol flap is, respectively, more fuel is supplied to the cylinder. Adjusting the carburetor of the brushcutter consists in setting the correct ratio of flaps to achieve the optimal consistency of the fuel mixture.

Lawn Mower Carburetor Working Principle

The throttle valve determines the amount of air to be supplied, and the engine power directly depends on this.

Fuel is sucked into the carburetor system by a pump (its membrane). Then it passes through the choke in the carburetor. The fluid then flows through the pump inlet and outlet valves. Filtered by the grid. Moves through the needle valve into the diaphragm chamber.

  • Air supply to a tube with an air baffle (damper). The baffle regulates the intensity of the air flow.
  • The fuel supply system is necessarily narrowed by a diffuser to increase the flow rate.
  • Gasoline through the float chamber and the nozzle tube with a constriction. A float chamber adjusts the temporary volume of gasoline. In the float chamber, the pressure level is neutral, and in the tube with a constriction it is already low. Due to the differential pressure, the fuel penetrates through the nozzle.
  • The acceleration of the air flow facilitates the transfer of fuel (gasoline) and its atomization. As a result, an air-fuel mixture of the required proportion or density is formed.
  • The air / fuel mixture enters the engine cylinder through the fuel pipe.

The level of air density in the system depends on the area of ​​the open air damper. The wider the throttle is open, the greater the fuel consumption and power.

Simply put, adjusting the carburetor on a petrol cutter. creating an optimal fuel mixture due to the correct air supply.

Broken primer

Primer is a mini hand pump for forced pumping of fuel into the carburetor. For a successful start of the engine, it may be necessary to pump 20 ml of gasoline manually.

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 the additional injection of gasoline.

adjust, carburetor, 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, since if it is incorrectly configured, it will either refuse to work, or will work intermittently and loss of power. Basically, engine tuning is about adjusting the fuel flow, and this is done using the grass trimmer carburetor.

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Failure of the adjusting lever

The wear of the contact edge of the lever is a consequence of an incompletely purified fuel, into which grains of sand 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.

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.

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.

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.

When to adjust

Carburetor adjustment is necessary in the following cases:

  • the new engine was run-in (4-5 liters of fuel mixture was used);
  • the composition of the fuel has changed (brand of oil and gasoline);
  • the weather has changed (it became hot, cold);
  • the rarefaction of air has changed (applies to mountainous regions);
  • after long-term storage;
  • increased load on the engine (after changing tools, etc.);
  • due to vibration, the adjustment screws spontaneously unscrewed;
  • fuel consumption has increased, the carburetor overflows fuel;
  • carbon deposits quickly appear on the spark plug electrodes (while the fuel mixture is prepared correctly);
  • the engine starts and immediately stalls or gains momentum poorly;
  • gasoline does not enter the cylinder;
  • large amount of exhaust gases.

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

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.
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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.

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.

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:

  • continuous operation of the grass 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.

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.
adjust, carburetor, trimmer

Also, the inlet needle may just jam.

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

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.