Trimmer Carburetor Adjustment BT 326

Despite the high productivity, mobility and unpretentiousness in work, modern lawn mowers are difficult to attribute to complex devices. Over time, any mechanism undergoes wear, and therefore parts and assemblies require special attention of the owner. One of the elements of the trimmer is a carburetor, designed to form a fuel mixture and its supply to the combustion chamber. Increased consumption with the correct proportions of gasoline and oil or a drop in engine power indicate the need to adjust the carburetor of the gas trimmer.

Trimmer carb setting

The initial step in restoring the correct operation of the fuel system is to clean the air filter.

Trimmer Carburetor Adjustment BT 326

Screw trimmer carburetor

Experts recommend rinsing it in a solution of water with detergents after every 10-15 hours. Direct adjustment of the trimmer carburetor is carried out by three adjusting screws:

  • Fuel feed adjustment screw (“L”);
  • Adjustment screw at high speeds ("H");
  • The screw responsible for idling the motor (“T” or “AT”).

Adjustment of fuel supply at the minimum turns

Before starting the carburetor adjustment of the gas trimmer, it is necessary to warm the engine to operating temperature.

Fuel Adjustment Screws

To do this, start the engine and at idle let him work 10-15 minutes. At the first stage, with the trimmer working, slowly tighten the screw “L” until the beginning of intermittent operation or until it dies. Next, unscrew the screw by ¼ turn and check the speed of maximum speed. If the lawn mower easily and quickly reaches high speeds, this will be the most economical mode. In most models on the market, the fuel screw “L” is turned clockwise, however, there are trim tabs where the decrease and increase in the mixture flow occurs in the reverse order.

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Trimmer idle adjustment

Location of carburetor adjustment screws

The screw "T" ("AT") serves as a limiter of the reciprocating movement of the fuel shutter and when it is twisted, the engine rpm increases, and turning it off leads to a decrease in the crankshaft speed. Professionals advise adjusting the idling screw of the lawn mowers so that the ICE works a little faster at minimum speed, but the head with the fishing line or knife remains motionless. If it is difficult to start the trimmer “cold” after the manipulations, then it is enough to tighten the “T” screw a quarter of a turn and try to start the engine again.

Adjustment of the screw of the maximum turns of a lawn-mowing

After restoring the fuel supply at minimum speed and adjusting the idle speed, it is necessary to check the stability of the mechanism at an increased speed.

Setting at maximum speed

Adjustment of the motor at high speeds is carried out in order to protect against overheating and reduce hand fatigue when pressing the accelerator key. If the internal combustion engine is unstable at maximum speed, then screw “H” must be slowly turned in to ensure smooth and clear operation.

During operation of the lawn mowers, it may be necessary to adjust the fuel feed screw (“L”) for an optimal set of revolutions.

Tips for repairing a gas trimmer carburetor

Video: Trimmer Carburetor Adjustment BT 326


  1. Regardless of the manufacturer, there is a factory defect of the carburetor parts of the lawn mowers.

Adjusting screw spring

For example, the adjustment procedure described above may not give positive results with an excessively large number of turns at the spring of the mixture feed screw and, as a result, the impossibility of optimally reducing the level of gasoline supplied. To eliminate this, you can independently shorten the spring yourself or purchase a new one in accordance with the instruction manual.

Many owners of lawn mowers when buying oil follow the recommendations indicated there for the preparation of the fuel mixture.

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Oil for gas trimmer

So, often the information on mixing gasoline and oil indicated on the bank differs from the instructions in the trimmer’s passport. As a result, a black deposit can quickly form on the spark plug, which leads to a drop in power and an increase in fuel consumption. Therefore, when preparing the working mixture, the recommendations specified in the instruction manual should be followed. In most cases, the proportion for a run-in ICE is 1:25. It is worth noting that many tool owners prefer to cook fuel “by eye”, which will inevitably lead to rapid wear of the piston spit in the event of a decrease in the portion of oil and the formation of soot on the spark plug with an increased amount of lubricating fluid.

  • The correct tips for setting up the trimmer carburetor correctly performed above will help to avoid not only engine overheating and increased fuel consumption, but also significantly increase the life of other parts and components of the tool. Pay attention to the operation of the lawn mowers in all modes and timely carry out regulated maintenance and repair of the tool.
  • Lawn mowers, like all gasoline powered tools for the garden, are not difficult to maintain. It is possible and necessary to repair, configure yourself. For example, adjusting the carburetor of the lawn mowers with your own hands is a matter of five minutes.

    Lawn mowing carburetor is a unit in the power system. In it, like any carburetors, there is a process of mixing air and fuel (gasoline) for further supply to the engine cylinders.

    The main problems and malfunctions of the carburetor.

    Strainer There are only two problems with this element:

    1. Clogging.
    2. Breakage

    In order to find out the cause of the breakdown, the fuel filter cover is unscrewed to remove the strainer. If dirt has simply accumulated on it, washing with gasoline or blowing will help.

    With visible damage to the strainer, it is imperative to install a new one. There may also be damage on the fuel supply pipe (during repair, check this element).

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    The carburetor starter in most cases does not function due to blockages. Use acetone or the same gasoline for flushing.

    Blowing off carburetor parts with a blockage of compressed air is an acceptable and convenient repair practice.

    The device of the carburetor lawn mowers

    The basis of the carburetor of the lawn mowers is an aluminum case. It has a diffuser (hole with internal contours). Air is blown through this hole. The oxygen (air) flow rate depends on the cross-section (passage opening) of the diffuser.

    The diffuser is equipped with fuel channels. Of these, fuel is drawn in using an air stream.

    Outside the carburetor is installed:

    • Fuel pump;
    • Jet system;
    • Fuel / air mixture control system;

    The principle of the carburetor lawn mowers

    The throttle valve determines the amount of air for supply, and engine power directly depends on this.

    Fuel is sucked into the carburetor system by a pump (its membrane). Then it passes through the fitting in the carburetor. Further, the fluid moves through the inlet and outlet valves of the pump. Filtered by mesh. The needle valve moves into the membrane chamber.

    Phased operation of the device:

    1. Air supply to the tube with an air baffle (damper). The partition controls the intensity of the air flow.
    2. The fuel supply system must be narrowed by a diffuser to increase the flow rate.
    3. Gasoline through the float chamber and nozzle tube with narrowing. A camera with a float adjusts the temporary volume of gasoline. In the float chamber, the pressure level is neutral, and in the tube with narrowing is already low. Due to the pressure drop, fuel enters through the nozzle.
    4. The acceleration of the air flow contributes to the transfer of fuel (gasoline) and its atomization. As a result, an air-fuel mixture of the necessary proportion or density is formed.
    5. The air-fuel mixture enters the engine cylinder through the fuel pipe.