Stihl Fs 55 Trimmer Carburetor Setup

The trimmer does not belong to complex household appliances, so most of its breakdowns are mechanical in nature and can be successfully repaired with their own hands. Even if the engine fails for serious reasons. Damage to the piston ring, for example, repair comes down to replacing the part.

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

Stihl Fs 55 Trimmer Carburetor Setup

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. Depending on the tool and its operating mode, mixing and feeding are adjusted accordingly.

The device of the carburetor is the same for almost all cases. It belongs to the category of float devices. The latter provide stable parameters of the finished mixtures.

The principle of operation of the module is as follows.

  • Air enters the body of the tube with an air damper. The latter enhances or reduces air flow depending on its position.
  • In the area where the hole for supplying gasoline is formed, the tube has a constriction. A diffuser. Here the flow rate increases.
  • Fuel from the float chamber through the nozzle is fed into the tube. The float level determines the amount of fuel supplied. Since the pressure in the chamber is normal and low in the tube due to the greater dilution of air, gasoline is sucked through the nozzle.
  • Accelerated airflow picks up fuel and atomizes it, forming an air-fuel mixture of the desired density.
  • The mixture is sucked into the cylinder through a pipe.

The more open the air damper in the tube, the higher the density of the air flow, which means that more fuel enters the cylinder. Setting up the carburetor of the brushcutter is reduced to setting such a ratio of dampers at which the density of the fuel mixture becomes optimal.

Signs of imbalance

Carburetor debugging is necessarily carried out in the manufacture of the apparatus. As a rule, the owners will only learn about the need to adjust the fuel supply with their own hands after serious enough failures, during the correction of which the module was removed and, for example, cleaned.

Signs of a failure in the settings are as follows:

  • It starts, but the engine stalls right away. Since the engine can only work when a certain amount of gasoline is supplied, if the fuel is too “poor”, that is, when the feed channel is blocked, the motor will stop;
  • Too much 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 turns out to be excessively dense.

The carburetor of the Stihl, Makita, Husqvarna and others brush cutters is adjusted using the adjusting screws. Sometimes the reason for the disorder of the work is a violation of fixation. Due to vibration or damage to the protective cap. Such a breakdown can be detected simply by trying to turn the screw a little: if the fixation is not rigid, it is worth checking the setting.

DIY carburetor adjustment

The configuration of the module does not apply to repair and replacement of spare parts is not required. In this case, a gas trimmer carburetor repair kit will not be needed.

There are three screws 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. With its help idle debugging is carried out.

There are options, as a rule, this is a Chinese petrol scraper carburetor, when there is only one screw left for debugging on the case. For setting idle speed. This does not mean that the module is automatically configured. It means that it will be difficult to carry out even a type of repair such as debugging. In the photo. The adjustment of the carburetor of the Chinese trimmer.

  1. Setting up the module is carried out only when the engine is warm: for this, the device is first turned on for 10 minutes. If the mowing head rotates at idle, then proceed with debugging immediately: turn screw T counterclockwise until the rotation stops.
  2. Adjustment starts with screw L. The screw rotates left and right until it finds its position at which idle speed does not become maximum.
  3. Then turn the screw на turn counterclockwise. This will be his working position.
  4. Idling must be adjusted by turning counterclockwise to increase the speed and clockwise to decrease. Its debugging consists in the achievement of such a mode in which a sufficient number of revolutions is made before the mowing head begins to rotate. In this case, the engine must work stably in different positions.
  5. The position of the screw L is determined last. At maximum speeds 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 established by ear.
  6. Then, the screw also rotates slowly counterclockwise until the motor starts to malfunction. Then the screw is turned back clockwise until the engine starts working again normally.

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

Adjustment of the carburetor of the brushcutter in the is carried out by ear.

7 comments on the record “Adjustment and repair of the carburetor of the petrol brush”

    Dmitry Pavlovich 07/04/2016

Please clarify. In the adjustment section 5, screw L. Error? Should I read screw A? Thank you

Tell me the initial position of the screws H L LA


Tell me the initial position of the screws H L LA

Thank you very much for the about the accelerator and I don’t know, and the defect is very important and creates a huge problem about which almost everyone is silent. Bravo….

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

And I have L, H, LA, is it LA instead of T?

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