Adjusting the carburetor of a Forte brushcutter

The device of the carburetor of the grass trimmer gasoline

Adjusting the carburetor of a brushcutter. a process that must be mastered for the full operation of the grass trimmer. 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 carburetor on a float-type brushcutter may require some fine-tuning. Nuances, due to the model and the specifics of its functioning, will provide a clear mode of mixing and feeding the fuel mixture.

Champion lawn mower carburetor, how to adjust it? This is just the grass trimmer of the float type. a common option, designed to mix in the provided proportions of air and fuel. The main problems that arise during the operation of the motor are roughly similar to the problems that overtake the carburetor in the car:

  • The engine may shut down as soon as it is started. The reason is that not enough gasoline is being fed. This is called “poor” fuel;
  • excessive gasoline supply leads to incomplete combustion, excessive mixture density and uneconomical consumption.
adjusting, carburetor, brushcutter

Carburetor Repair

Important! You have to adjust the carburetor under different circumstances: after a change in temperature, fuel octane or oil type, after the winter or the end of the running-in period, after loading or if the screws turn by themselves because of severe vibration of the body. Some owners prefer to tune the module before each use to make sure it works properly.

Adjusting the lawn mower carburetor: the main points

Despite their high output, mobility and unpretentiousness, modern brushcutters are hardly the most complicated machines. Over time, any mechanism is subject to wear and tear, and therefore the parts and units require separate attention of the owner.

One such element of the grass trimmer is the carburetor, designed for the formation of the fuel mixture and its supply into the combustion chamber.

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

Grass trimmer carburetor adjustment

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

Experts recommend after every 10-15 hours to wash it in a solution of water and detergents. Direct adjustment of the grass trimmer carburetor is performed by three adjusting screws:

  • Fuel adjustment screw (“L”);
  • Adjustment screw at high revs (“H”);
  • the screw responsible for the work of the motor at idle (“T” or “AT”).

Adjustment of fuel supply at minimum rpm

Before adjusting the carburetor of the gasoline triimeter the engine needs to be warmed up to working temperature.

For this 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.

Loosen the screw by ¼ of a turn and check how fast you can reach the maximum rpm. If the mower quickly and easily reaches high revolutions, this is the most economical working mode.

In most models on the market, the fuel screw “L” is turned clockwise, but there are trimmers for grass, where the reduction and increase the flow of mixture occurs in reverse order.

Grass trimmer idle speed adjustment

Adjustment screws for carburetor

Screw “T” (“AT”) serves as a restrictor of reciprocating motion of fuel valve and by tightening it the engine rpm is increased, and unscrewing it results in decreased rotational speed of the crankshaft.

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

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

Maximum RPM screw adjustment on the brushcutter

After recovery of fuel supply at minimum RPM and adjustment of idle speed it is necessary to check stability of operation at higher RPM.

Adjustment of the high engine speed to protect against overheating and to reduce hand fatigue when pressing the gas pedal button. If the engine is working erratically at maximum RPM and you need to turn the “H” screw slowly until you get a smooth and responsive performance.

You may need to readjust the throttle trigger (“L”) when operating the brushcutter for optimum RPM.

Tips for repairing the carburetor of a gasoline trimmer

For example, the adjustment procedure described above may not give a positive result, if the number of turns of the mixture screw spring is too large, and therefore the optimal reduction of the fed petrol level is impossible. To correct this, you can shorten the spring on your own or buy a new one according to the instruction manual.

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So, often the information on mixing gasoline and oil indicated on the bank differs from the instructions in the trimmer’s certificate for grass. As a consequence, black carbon deposits can quickly form on the spark plug, which leads to a drop in power and increased fuel consumption.

Therefore, when preparing the working mixture, you should follow the recommendations specified in the operating manual. In most cases, the proportion for the running-in engine is 1:25.

It is worth noting that many tool owners prefer to “by eye” prepare fuel, which will certainly lead to rapid wear of the piston grasshopper in the case of reduced oil portions and the formation of carbon deposits on the spark plug with an increased amount of lubricating fluid.

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

Grass trimmer device

The float-type carburetor consists of an aluminum housing with a hole (diffuser). The air is pumped through the air inlet, and gasoline is drawn in through the fuel ducts along with the air flow. This is the base of the device. the fuel chamber. Top-mounted jets, a pump and a mixture control system ensure not only saturation but also an even flow of fuel.

For your information! The float carburetor has been used for decades, and the basic problems with all types are similar. The principle of operation of the device depends on the quality of the mixture, and the adjustment is aimed at providing it.

The construction of the lawnmower carburetor

The basis of the lawnmower carburetor is an aluminum housing. It contains a diffuser (orifice with internal circuits). Through this hole the air is pressurized. On the cross-section (flow opening) of the diffuser depends on the rate of oxygen (air) supply.

The diffuser has fuel lines. From them the fuel is drawn in by the flow of air.

Adjusting the carburetor

Flush the air filter before adjusting the carburetor. It is recommended that you flush it after every 10 hours of operation. After that you can start adjusting. The example photo shows the carburetor on the PRORAB-8406 gasoline grass trimmer. The numbers indicate the adjustment screws that we will use.

Adjustment screws of the carburetor of the PRORAB-8406 gasoline grass trimmer

Start the lawn mower and wait for it to warm up.

Check how the engine revs up by opening the throttle. Continue loosening the screw a quarter turn at a time until the engine starts to steadily pick up higher revolutions when starting up. This will be the moment of the most economical stable operation of the engine. At petrol grass trimmer PRORAB-8406 adjusting screws are screwed clockwise, unscrewed. against, at some other brands of petrol brush can be the opposite.

Now adjusting the lower speed. Screw limits the throttle lever return motion. by screwing it in, we increase idle RPM, by unscrewing it. we decrease. Adjust so that the engine runs solidly at a low RPM and even a little faster (for a better start), but that the line spool or knife does not rotate and has enough RPM to spare before it starts turning. If the engine starts poorly, increase the idle speed even more.

After adjusting the fuel mixture and low speeds, check how the mower engine will run at maximum rpm. If necessary, limit the maximum rpm to the desired level with the hollow screw Loosen the locking nut and screw in to reduce the maximum rpm or unscrew to increase.

In the future it may be necessary to adjust the grass trimmer carburetor. For example, if the engine at full load begins to poorly gain speed, turn the screw a quarter turn more. If it is difficult to start, increase the idle speed. Weather conditions and fuel mixture quality can also affect mower performance. Vibration may cause the adjusting screws to turn.

Diagnosis and adjustment of the carburetor with their own hands can take only a few minutes.

To get it right, start the engine. Your procedure is as follows.

  • Find the idle speed limit. To do this turn the screw L to the right and then to the left. Turning step. a quarter turn counterclockwise.
  • you can adjust the motor idle speed with the screw T: go clockwise if you turn it clockwise and anticlockwise if you turn it back. The engine is running smoothly with no load and no warm-up. When warmed up. does not overspeed.
  • If you are not adjusting a brushcutter, but a grass trimmer, the turns of the T screw set a larger reserve of revolutions per minute. For both types of devices, set a steady RPM while selecting a blade (or fishing line) cutting height.
  • The last screw to turn is the H screw. It sets the rate of petrol and air at close to maximum rpm, engine power, engine temperature and fuel consumption.

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

Open the throttle and squeeze the gas at maximum rpm. Turn the H screw clockwise until the engine rpm drops. Turn the same screw slowly counter-clockwise until the engine spikes at a steady RPM. Turn the screw back a little (clockwise) until the motor runs straight

It’s important to catch this edge. Precise adjustment results in complete combustion and a brownish, white spark plug color

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A spark plug filled with petrol is much darker than a spark plug that is not

the result of the fine adjustment is complete combustion and a white-brown spark plug color. A spark plug filled with gasoline is much darker than a spark plug that is not filled.

How to adjust the carburetor of a lawn mower, see below.

Reasons for carburetor malfunctions

When using a brushcutter (for example, “Patriot” or “Soyuz”), the carburetor can be damaged, and the user will need to repair it by himself or with the help of specialists. This can occur for a number of reasons. One of the most common is failure to follow the rules for using the device. If the carburetor was not serviced and adjusted during prolonged use of the grass trimmer, the device will break.

Another cause of breakdown. improperly prepared fuel mixture. Often machine owners buy oil and prepare fuel according to recommendations written on the package of fuel and lubricants, which is wrong. When preparing fuel it is important to follow the instruction manual of the brushcutter. In addition, you should not make the mixture “by eye”, as incorrect proportions also lead to a breakdown of the technique.

Important! Lawn mower malfunctions when using poor quality fuel or if the fine filter is damaged and/or clogged. or dirt in the carburetor chamber.

Most carburetor failures are the same for different brands of brushcutters, whether it’s an Echo, Kedr, Homelite or a device from another manufacturer.

How the lawnmower carburetor works or how it functions

Adjustment of the carburetor of a Chinese lawnmower is completely identical to the adjustment of lawnmowers of European, Russian and manufacturers. To cope with the task of adjusting the carburetor on gasoline mowers and gasoline trimmers, it is necessary to understand how they work. How the carburetor works on a chainsaw, step by step and accessible described below.

  • The operation of the lawnmower carburetor begins with the fuel supply through the channel, as shown in the diagram
  • Fuel is drawn into the carburetor by means of an impulse conduit connected to the engine crankcase. Due to rarefaction of air there is a movement of flexible diaphragm under number 4 in the diagram above
  • Fuel supply occurs through valves 3 and 5. Valve 3 is the inlet valve that moves fuel into the space below the diaphragm and valve 5 is the outlet valve
  • Fuel then travels along the channel and, passing through the fine filter, reaches the needle valve 14
  • The needle valve is connected through a lever to the pilot diaphragm 18
  • The needle valve is actuated by acting on the diaphragm. When it is necessary to prime the fuel to start the engine, it is necessary to act on the soft cover of the hand pump. The needle is actuated to open the needle and fill the chamber with fuel mixture
  • When the engine is started (in cold conditions) the needle opens due to rarefaction with the closed air valve. This negative pressure acts on the diaphragm at idle and high speed through the nozzles 18
  • The diaphragm acts on the needle valve through the lever and the chamber fills up
  • When the engine starts, the choke opens and the engine runs on a lean mixture as the fuel is mixed with the air
  • Fuel mixture when the chamber is full is fed (sucked) through the nozzles at idle and medium speed (when the engine is started)
  • The butterfly valve moves approx. 10-15 degrees from its original position
  • When work is carried out under load, the fuel begins to arrive in the chamber through the nozzle at high speed, and the throttle valve is rotated to an angle of 90 degrees (depending on the force of pressing the gas). In all operating modes, the air damper must be open, through which fuel is mixed with air, and thus the mixture is ignited in the cylinder

The diagram of the principle of the lawnmower carburetor is shown below. On the basis of the diagram you can not only understand the principle of operation, but also to identify breakdowns and other malfunctions of the mechanism.

When operating the tool, it is necessary to take into account the presence of another junker. This jammer is located between the idle and full power channels. It is necessary in order to avoid a strong depletion of the mixture, which occurs when the engine works at partial load. In such a situation, it is not ruled out that scoring of the pair can occur. The additional rail (refueling nozzle) sucks fuel into the chamber and thereby enriches the fuel-air mixture. The scheme below shows an additional nozzle, which is marked with the number 1.

Having an idea of the design of the membrane carburetor of a brushcutter and the principle of operation, it will not be difficult to make its adjustment with your own hands. To adjust the carburetor of the lawnmower use the adjusting screws. The diagram above shows two screws for adjustment, but most modern models of gasoline trimmers are equipped with three screws. The presence of three adjusting screws allows you to make more precise adjustment, while achieving stable and smooth operation of the engine.

This is interesting! What’s the difference between a trimmer and a chain saw?? Many people think that grass trimmers are low-powered electric mowers. However, grass trimmer. this is a generalized name for gasoline lawnmowers, brushcutters and electric mowers, as they are designed for common purposes.

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Step-by-step instructions for repairing the carburetor of a brushcutter

To disassemble the carburetor

Visual inspection of the carburetor will help identify fuel leaks and air suction, but the main causes of device failure lie inside. Therefore, in order to determine and most importantly fix the failure, the carburetor must be disassembled.

It doesn’t take much to disassemble the brushcutter carburetor.

You just have to unscrew the four screws on one side

and two with the other. You can do it with a normal Phillips screwdriver. Carefully unscrew the screws and put them aside. You may need it for reassembly. It is a good idea to drape the table with a white cloth so that all, even the smallest parts, which may fall out before disassembly, are visible.


Start disassembly from the side of the fuel system.

We remove the primer. the primer bubble, which is noteworthy, when assembling the carburetor parts are simply impossible to install incorrectly. The products have characteristic castings and holes.


Now you need to remove the diaphragm. It performs the function of pumping the fuel into the carburetor.

When the membrane vibrates, the other side exerts pressure on the rocker mechanism and the needle rises, which, in turn, opens the hole and the fuel is fed.


Let’s take off the carburetor cap with the injection mechanism.


Next, another diaphragm is installed. Remove it carefully.


Under the diaphragm there is another gasket. Remove it with care, without damaging it in any way.


Next we proceed to the dismantling of parts from the back of the carburetor. As said before unscrew the two bolts. This is the air supply system.

Here is a slide, which, when you add “gas” opens and increases the flow of air into the engine.

After removing it, we are left with the bare housing in our hands. The carburetor is disassembled.

Trouble shooting and troubleshooting

Now it is worth paying attention to the problems that occur during the operation of the carburetor and ways to fix them.

Problem 1: Dirt clogging the holes, ducts and jets

The first thing that happens is that the holes and jets in the fuel system get clogged with dirt. The filters installed in the tank and directly in the carburetor don’t help. But they do let in small particles and these cause the brushcutter to malfunction.


To do this, unscrew the bolt on the mechanism, holding it with your finger. The thing is that there is a spring there and a careless action will cause that it is lost.


How to do the flushing. The most effective way is to use ultrasonic bath.

It is filled with either a special liquid or gasoline, the carburetor is placed there, and under the influence of ultrasound, the so-called cavitation effect, the channels are cleaned of dirt.

The second option of cleaning with compressed air.

You can use, available in the household, a compressor and perform cleaning of the carburetor channels. However, this method is effective if the contamination is not very large.

If you do not have at hand an ultrasonic bath or a compressor, you can perform cleaning in the third method with a special cylinder for cleaning the carburetor. They are available in almost all auto stores and supermarkets. Price is low and equals about 2-3 Has such a can for 4 or 5 blowouts.

Step 0

Now we need to purge the channels in the body and carburetor cover. See picture.

Step 1

Another particle of dirt can be trapped under the needle. See. photo. This also causes the brushcutter to malfunction.

Important! Never use pins, needles or wires for cleaning the carburettor. Even the slightest scratch will kill the carburetor. You’d have to replace the whole thing.

Problem 2: fine filter is clogged

It is located on the carburetor cover and is a fine metal mesh. It becomes clogged very often. It is connected with sedimentation of oil, additives and dirt on it.

adjusting, carburetor, brushcutter

Step 2

Sometimes disassembly reveals a certain film on the mesh. That causes the carburettor to get low on fuel and the lawnmower either does not start or works irregularly. Cleaning methods are identical to the first reason: ultrasonic bath, compressor or a can with a special solution. In addition, if the mesh is clogged thoroughly it is necessary to take a soft watercolor brush, soak it in gasoline and gently rinse it without damaging.

Step 3

They have the ability to wear out with use. From prolonged use they deform, stretch, lose elasticity, poor quality fuel corrodes them, and can no longer perform their functions well. This also applies to the needle itself. The fact is that it is covered with a thin layer of rubber, which in the process of work wears out and can no longer fit tightly into the hole. The lawnmower begins to work intermittently. To fix this problem it is necessary to replace all worn out parts. Where to get them?

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