How to adjust the carburetor on a brushcutter. Adjusting the lawnmower carburetor can be done with your own hands

The device of the carburetor of the grass trimmer gasoline

Adjusting the brushcutter carburetor. a process that must be mastered for the grass trimmer to work fully. Grass trimmer. a completely uncomplicated device, which can break only in a few places and require mechanical repair or replacement of the part. Adjusting the float-type brushcutter carburetor device may require knowledge of certain subtleties. The nuances due to the model and the specifics of its operation will provide a clear mode of mixing and feeding the fuel mixture.

Champion lawnmower carburetor, how to adjust? This is just a float-type grass trimmer. a common option, designed to mix in the prescribed proportions of air and fuel. The main problems that occur with the motor are roughly similar to the problems that plague the carburetor in a car:

  • the engine may stall as soon as you manage to start it up. The reason is that gasoline is not supplied in sufficient quantity. This is called “poor” fuel;
  • Over-fed petrol leads to incomplete combustion, excessive mixture density and uneconomical consumption.

Repair of the carburetor

Important! Adjust the carburetor has to under different circumstances: a change in temperature mode, the octane number of fuel or type of oil, after winter or the end of the running-in period, load or spontaneous turning of the screws from strong vibration of the housing. Some owners prefer to tune the module before each use to make sure it works correctly.

Adjusting the lawn trimmer carburetor: highlights

Despite their high performance, mobility and unpretentiousness in operation, modern brushcutters can hardly be classified as complicated devices. Over time, any mechanism is subject to wear and tear, and therefore parts and assemblies require special attention of the owner.

One such element of the grass trimmer is the carburetor, designed to form the fuel mixture and feed it into the combustion chamber.

Increased consumption when the correct proportions of gasoline and oil or a drop in engine power indicate the need to adjust the carburetor of the gasoline trimmer for grass.

Adjusting the grass trimmer carburetor

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

adjust, carburetor, brushcutter, adjusting

Experts recommend that after every 10-15 hours to wash it in a solution of water with detergents. The direct adjustment of the grass trimmer carburetor is made with the three adjusting screws:

  • Fuel adjustment screw (“L”);
  • high speed adjustment screw (“H”);
  • The screw responsible for idling the motor (“T” or “AT”).

Adjustment of fuel supply at minimum rpm

Before beginning to adjust the carburetor gasoline trimmer requires warming up the engine to working temperature.

To do this we start the engine and let it idle for 10-15 minutes. On the first step, with the trimmer running, slowly turn the “L” screw until intermittent operation begins or until the trimmer stalls.

Then we unscrew the screw by ¼ of a turn and check the set speed of the maximum revolutions. If the mower quickly and easily reaches high revolutions, this is the most economical mode.

Stihl Carburetor Tools You Need For Chainsaws, Weedeaters, Leaf Blowers etc.

In most models available on the market the fuel screw “L” is tightened clockwise, but there are grass trimmers where the reduction and increase of mixture inflow occurs in the opposite order.

Grass trimmer idle speed adjustment

Position of the carburetor adjustment screws

Screw “T” (“AT”) serves as a restrictor of reciprocating motion of the fuel valve and tightening it increases engine speed, and unscrewing it reduces the speed of the crankshaft.

Professionals advise to adjust the lawnmower idle speed screw so that the engine works a little faster at minimum rpm, but the head with the line or the blade remains stationary.

If after the manipulation it is difficult to start the grass trimmer “in the cold”, it is enough to turn the screw “T” a quarter of a turn and try to start the engine again.

Adjusting the maximum rotational speed screw on the brushcutter

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

High RPM setting is used to protect the engine from overheating and reduce hand fatigue when pressing the gas pedal button. If the engine is working erratically at maximum RPM, the “H” screw should be turned slowly until smooth and even operation is assured.

When using your brushcutter it may be necessary to readjust the “L” screw for optimum RPM.

Tips for repairing a gasoline trimmer carburetor

For example, the adjustment method described above may not give positive results when the number of coils at the mixture feed screw spring is too large, and as a consequence, the optimal reduction of the fed gasoline level is impossible. To eliminate this, you can independently shorten the spring a little or in accordance with the instruction manual to buy a new.

So, often the information on mixing gasoline and oil on the can differs from the instructions in the certificate of the trimmer for grass. The consequence is that black carbon deposits can form quickly on the spark plug, resulting in reduced performance and increased fuel consumption.

When preparing the mixture, it is therefore necessary to follow the recommendations given in the Operation Manual. In most cases, the ratio for a running-in engine is 1:25.

It is worth noting that many owners of the tool prefer to “by eye” to prepare fuel, which will certainly lead to rapid wear of the piston grass trimmer in the case of a decrease in the oil portion and the formation of soot on the spark plug in the case of an increased amount of lubricating fluid.

Adjusting the lawn mower carburetor: highlights was last modified: June 25th, 2018 by Admin

Main malfunctions

Troubleshooting the carburetor of brushcutter or grass trimmer, despite the relative ease of fixing them, sometimes require a long search by the method of elimination. The main causes are as follows:

Fuel injector malfunction

The most recurring failure is diaphragm wear, rupture. The consequence is that it does not fit. Fuel passages are not sealed at certain stages of the engine cycle. The causes are as follows:

  • you work too long on your brushcutter or trimmer without a break;
  • poor-quality fuel is filled;
  • Exhaust gases enter the pulse channel.

A deformed diaphragm has several bad consequences:

adjust, carburetor, brushcutter, adjusting

Carburetor Adjustment. Everything You Need to Know

  • Not enough gasoline or oxygen in the combustible mixture created;
  • engine starts after 10 or more unsuccessful attempts;
  • engine knocks, clangs when running, etc. д.;
  • The operating piston deforms.

As a result, the inner space of the fuel pump gets dirty on the impulse channel side.

Plugged filter

Causes of clogged strainer. poor quality fuel cleaning, damaged hose and/or discharge head.

Failure of the adjustment lever

Wear of the lever’s contact surface, which is a consequence of insufficiently purified fuel with grains of sand, clay or metal particles or other inclusions insoluble in liquid hydrocarbons. Fuel injection problem appears, engine operates irregularly without load.

Inlet needle is defective

Inlet needle breaks because of metal particles and stone in gasoline. As a result, the seat of the inlet needle does not fit tightly, the fuel mixture leaks. There is too much air in the mixture created by the carburetor and the engine may sneeze while running. Finally, the needle may be blocked because of poor-quality gasoline or the unit has been idle for a long time.

Clogging of the adjusting space

Deposits may accumulate in the adjusting compartment. The needle does not close the hole completely and a lot of gasoline enters the fuel chamber. the engine overflows it, possibly flooding the spark plugs as well. The gasoline-air mixture contains an excessive amount of gasoline vapor. Efficiency drops noticeably.

Control diaphragm is ruptured

The diaphragm is often deformed (sometimes even torn) due to continuous operation of the brushcutter or grass trimmer for several hours. If you abuse this “shock” mode of operation, damage to the diaphragm is more common. New breakages will appear from the horn of plenty:

  • The piston will break;
  • the number of unsuccessful attempts to start the engine will drastically increase;
  • the fuel mixture will contain too little petrol;
  • useful (thermal) power will drop down drastically.

Inlet adjusting lever gets stuck

Adjustment lever jams due to improper installation, accidental bending. The contacting facet gets the wrong position. It will interrupt the auxiliary flow of gasoline.

The choke is worn out

Throttle valve and air valve become unusable because of dust, metal particles etc. in the air flow. д. Damaged flaps look like parts that have been blasted with sand. Wear of the throttle valves reduces the efficiency of the engine and causes the engine to break down. Piston and cylinder wear out.

Damage to the slide gate due to improper maintenance or a broken air filter.

The filter may not be compatible with your brushcutter or trimmer model. Eventually the motor shaft will suffer. pieces of it will get into the engine channels, causing the piston to break.

The carburetor cannot be adjusted

If the adjustment is too rough (no exact setting), the springs on the adjusting screws are to blame. Excessively thick and stiff springs may have been supplied by the manufacturer of the brushcutter or grass trimmer. You can find others either in shops that repair such equipment, or purchase from any dealer or an official representative of the company that produced the motor for your trimmer for grass or a mechanical grass mower.

The primer is broken

Primer is a manual mini pump for forcing fuel into the carburetor. It may be necessary to pump 20 ml of gasoline manually to successfully start the engine.

The carburetor is built

lawnmower (lawnmower) contains a base. a housing made of aluminum, in which the other parts are placed, working together as a single unit. The carburetor body has a diffuser, a stroke with internal channels through which air is pumped.

The larger the cross section of the diffuser, the more active together with the air is the oxygen. oxidizer, in which the fuel (gasoline and oil mixture) burns.

Channels branching off the diffuser stroke deliver fuel, with which the injected air mixes, entrapping gasoline vapors. Outside the main compartment of the carburetor are placed:

The carburettor on the lawnmower

The basis of the lawnmower carburetor is an aluminum housing. There is a diffuser (hole with internal circuits). The air is pumped through this hole. The oxygen (air) flow rate depends on the cross-section (orifice) of the diffuser.

The diffuser is equipped with fuel ducts. The fuel is sucked out of them with the help of an air stream.

Adjusting the carburetor

The next step is to adjust the idle speed. And to do this, little by little unscrew the extended nut, which is needed to pull the cable when you press the gas pedal button on the handle.

The point of this adjustment is to achieve optimum freedom of movement. it should not be more than 2 mm.

This setting should cause the choke to open more or less fully when the gas pedal button on the handle is pushed. Screw the second nut all the way in. So let’s stop the whole thing.

The next step is to adjust the gasoline screw. We tighten this screw to the end, and then unscrew 1.5 turns.

Install the housing with an air filter, screw in the spark plug and then try to start a brushcutter. If everything is fine, continue tuning.

Troubles and fixing them

Electric and gasoline trimmers have typical breakdowns and malfunctions. For devices powered by the internal combustion engine, it is:

  • Problems in the carburetor;
  • engine failure;
  • Fuel system problems;
  • breakage of the gearbox, starter, muffler;
  • clogs;
  • breakage of the air filter;
  • Problems with the ignition coil.

Electric units have specific breakdowns:

If the problems are not complicated, you can do the grass trimmer repair with your own hands.

Why does not the grass trimmer start?

The most common reason that the unit won’t start is the use of poor-quality fuel. The choice of gasoline brands below AI-92 can disable the lawnmower. If quality fuel is used, you need to look for other causes. To do this, thoroughly check all nodes and systems. Subject to inspection:

The unit may not start after a long period of idle time. Before turning on the trimmer for grass, you need to carefully study the instruction manual. There are solutions to many of these problems.

If it stalls when you press the gas

There are several reasons why the grass trimmer stalls when the throttle is pressed:

  • The first reason is a carburetor misalignment.
  • Clogged fuel valve.
  • Clogged check valve.
  • Loose or slack carburetor cable or slack fuel hose.

To avoid the described problems with the lawnmower, you need to carefully monitor the condition of the device and its units. Timely cleaning, washing of the unit and spare parts allows you to increase its working life.

Starter failure

The most difficult breakdown of the starter occurs when the rope breaks and winds it on the flywheel of a running engine. As a result, the spring may burst and tear the pulley. In this case, only a complete replacement of the part will help. Such a breakdown occurs rarely. often happens:

In this case, it is easy to repair the starter itself. The manufacturer has prepared step-by-step instructions for this.

Gearbox Repair

To maintain a brushcutter gearbox, it must be lubricated in time. Lack of it can lead to rapid wear of gears and jamming of the gear module.

The main malfunctions of the grass trimmer gearbox:

  • High heating of the transmission unit due to the use of low-quality lubricant or lack of it;
  • The shaft is seized by the rotation of worn bearings;
  • Wobbling or falling off the transmission mechanism rod as a result of damaged housing;
  • No rotation of the output shaft with a knife due to the wear of teeth on the gears.

This happens due to the use of low-quality lubricant or its complete absence. Another cause of gearbox failure is the operation of the grass trimmer at its limits and the ingress of foreign objects. To replace a faulty bearing, disassemble the gearbox.

Peculiarities of repair of electric models

Electric models of trimmers, working from the network, have several main blocks in their composition:

Each unit of the electric trimmer has specific malfunctions. In the mechanical part, they depend on the presence of a fishing line used as a cutting element. Causes of stoppage of work:

Detect problems with the electric part of the electric mower can be identified with the help of special tools:

A blowtorch is needed to fix problems.

  • Faulty power cable;
  • Problems with the socket and plug;
  • Control knob failure;
  • burned winding of the starter, requires replacement of the motor;
  • broken contacts can be repaired by yourself with a blowtorch.

How the lawnmower carburetor works

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

Fuel is sucked into the carburetor system by the pump (its diaphragm). Then flows through the nozzle on the carburettor. The fluid then moves through the inlet and outlet valves of the pump. Is filtered by the wire mesh. The needle valve moves into the diaphragm chamber.

adjust, carburetor, brushcutter, adjusting
  • Air supply to the tube with an air baffle (damper). The baffle plate controls the intensity of the air flow.
  • The fuel system is necessarily narrowed by a nozzle to increase the flow rate.
  • Gasoline through the float chamber and nozzle tube with constriction. The float chamber regulates the temporary volume of gasoline. In the float chamber, the pressure level is neutral, but in the narrowed tube, the pressure level is already low. Through the pressure differential the fuel flows through the nozzle.
  • Acceleration of air flow promotes the transfer of fuel (gasoline) and its atomization. As a result, an air-fuel mixture of the desired proportion or density is formed.
  • The air-fuel mixture enters the engine cylinder through the fuel tube.

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

Simply put, the adjustment of the carburetor on a gasoline mower is to create an optimal fuel mixture by correcting the air supply.


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

  • replacement of the fuel pump;
  • disassembly and washing of the strainer;
  • replacement of the adjusting lever;
  • It is also necessary to clean the adjustment space;
  • replacement of the diaphragm (or the entire unit where the diaphragm is located);
  • adjusting the intake, exhaust and needle valves;
  • replacement of the flaps;
  • cleaning the fuel ducts and diffuser;
  • replacing the screw springs;
  • primer change.

Not all of this work can be done. It often turns out that many of these are not necessary if a particular fault is detected immediately.