Trimmer Stihl Petrol Carburetor Adjustment

Chainsaw Stihl 180. device and carburetor adjustment

The stihl ms 180 chainsaws are designed in such a way as to make their operation as easy as possible for inexperienced users. To this end, some of the settings available on the more powerful Stihl models were abolished in the saw carburetor. But there is still an opportunity to configure, and repairs, as well as adjusting the carburetor of the Stihl 180 chainsaw with your own hands, is possible.

Trimmer Stihl Petrol Carburetor Adjustment

Adjusting the Stihl 180 carburetor

The carburetor of the Stihl 180 chainsaw, indiscriminately, can only be adjusted for the number of idle revolutions. It is impossible to increase or decrease the fuel supply in different modes using special screws. The manufacturer restricts access to adjustments and does not install these screws. How to adjust the carburetor to the correct idle speed is described in great detail in the manufacturer’s instructions.

In the event of certain malfunctions, and with experience, it is possible to increase or decrease the fuel supply by increasing the clearance when opening the needle valve.

To increase the flow, the rocker arm of the needle valve in the distribution chamber must be bent up, and to decrease, down. This regulates the stroke of the needle and, accordingly, the throughput of the valve.

Air damper

The carburetor choke is installed on the opposite side of the throttle and is responsible for starting a cold engine, it is controlled by the engine control lever. For a cold start, the air damper is completely closed, for normal operation, open.

Fuel pump

A fuel pump is installed directly in the carburetor body, which operates under the action of an air pulse from the crankcase of the chainsaw, which is transmitted through special channels. A diaphragm is installed in the pump, it is she who is responsible for pumping fuel under the action of an impulse. A gasket is installed between the diaphragm and the body, which is responsible for the tightness of the fuel pump.

When to adjust the Stihl 180 carburetor

To begin with, it is worth deciding why it may even be necessary to adjust and repair the stihl ms 180 carburetor. So, this must be done in the following cases:

  • If the chainsaw does not idle;
  • Repairs may be required if the saw does not start;
  • Power loss is observed;
  • Increased fuel consumption;
  • Chainsaw does not reach maximum rpm.
  • Stalls when accelerating.

This list can be continued for a long time, but we have identified the main reasons. Before proceeding with the adjustment, you need to know what are the main parts of the carburetor on the Stihl 180 chainsaw, and who makes it.

Removal and installation algorithm

In cases where it is necessary to clean the Stihl 180 carburetor or disassemble it, first you need to remove the assembly from the chainsaw. This must be done in compliance with a certain algorithm of actions:

  • Put the protective cover for the chainsaw on the tire.
  • Remove the top cover of the chainsaw.
  • Remove the two nuts securing the air filter and carburetor.
  • Remove the air filter housing.
  • Disconnect the wire from the engine control lever.
  • Carefully remove the lever from its seat in the housing, at the same time disconnecting the air damper rod from it.
  • Pull the carburetor towards you and disconnect the fuel supply as well as the throttle rod.

To facilitate dismantling, you can additionally untwist the rear handle and disconnect the throttle rod first from it, and then only from the carburetor. This may be required, because without some experience, disconnecting the rod from the carburetor is quite problematic and it is easier to first disassemble the handle.

To install the part in place, follow the reverse order of the algorithm.


The fuel injector is mounted in the carburetor body in such a way that it is a connecting link between the distribution chamber and the cavity in which the throttle valve is installed. Simultaneously with the fuel, air is supplied to the nozzle and an air mixture is formed. The injector has a check valve that blocks the flow of air in the reverse sequence, that is, from the throttle chamber to the distribution chamber.

Distribution chamber

In the distribution chamber, as in the fuel pump, there is also a membrane that opens and regulates the fuel supply by pressing a special rocker, while raising its needle valve.

The cover of the chamber is the compensator body, which is attached to the carburetor with four screws, a gasket is installed between the body and the cover, which increases the height of the chamber and is responsible for sealing.

Frequent breakdown of the Stihl carburetor and how to avoid it

A common reason for the failure of the carburetor on the Stihl chainsaw is a sticking valve in the nozzle. The reason for sticking is a violation of the storage of the chainsaw, or rather the instructions of the manufacturer Stihl 180 for proper preparation for storage.

As follows from the instructions, before long-term storage, it is necessary to drain the fuel from the tank, then start the saw and burn the gasoline from the carburetor. Failure to comply with this elementary rule entails the following consequences. The forsknui valve, being in direct contact with the fuel, sticks to the body, since the gasoline evaporates little by little and only sticky oil remains. It is impossible to replace the nozzle, because they are not in the repair kit, you can only try to knock it out and rinse it, which is not always possible to do without damaging the nozzle.

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Common carburetor malfunctions

Failure of the trimmer carburetor occurs due to the use of poor quality gasoline, a damaged air filter and the 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 lawn mowers carburetor malfunctions.

Intake Adjust 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.

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:

  • Long work of the trimmer;
  • Use of unsuitable fuel;
  • Gases entering the impulse channel.

As a result, diaphragm damage reduces pump performance and, as a result:

  • Depletion of the combustible mixture occurs;
  • Difficulty starting the engine;
  • There are interruptions in the operation of the motor;
  • The piston is damaged.

Also, the above-described consequences for the motor 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.

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.

Due to the ingress of poorly cleaned air, the shaft wears out and may 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.

How to properly adjust the 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 it will work intermittently and loss of power. Basically, engine tuning is about adjusting the fuel flow, and this is done using the carburetor trimmer.

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 air rarefaction has changed (applies to mountainous regions);
  • After long-term storage;
  • The load on the motor has increased (after tool change, etc.);
  • Due to vibration, the adjustment screws unscrewed spontaneously;
  • 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 up and immediately stalls or gains momentum poorly;
  • Gasoline does not enter the cylinder;
  • Large amount of exhaust gases.

Adjustment lever defective

This breakage occurs when the contact surface of the lever wears out.

The abrasion of the contact surface occurs due to the presence of abrasive particles in the gasoline or due to strong vibration of the engine during operation. This defect in the adjusting lever causes problems with the intake, as well as improper idling of the engine.

Deformation of the control diaphragm

The membrane can undergo deformation during prolonged operation of the unit and when using aggressive fuel.

Failure to perform normal adjustment due to a defect leads to:

  • Damage to the piston;
  • Difficulty starting up;
  • Depletion of fuel;
  • Improper engine operation.

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 violated;
  • Leakage of the combustible mixture appears;
  • There are malfunctions in the operation of the engine associated with re-enrichment of the fuel mixture.

Also, the inlet needle may just jam.

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

Idle speed adjustment

We start adjusting low speed. Screw number 2 limits the return movement of the throttle lever. by turning it, we increase the idle speed, unscrewing it, we decrease it. Adjust so that the engine runs confidently at low revs and even slightly accelerated (for better starting), but so that the line reel or knife does not rotate, and there is a sufficient reserve of revolutions before they start spinning. If the engine starts poorly, increase the idle speed even more.

lawn mower or trimmer

A trimmer is a broader concept than a lawn mower (lawn mower), as it can also be electric. A petrol trimmer and a lawn mower are one and the same.

Some authors claim that the trimmer is a weaker tool than a more powerful lawn mower, which can be used for mowing shrubs. Personally, I have a tool with a maximum power of 1.7 kW and is capable, as stated in the instructions, of mowing small shrubs up to 10 mm thick. The user manual is called “Petrol trimmer.”.

Fuel ratio

I read somewhere that if different mixing ratios are indicated in the operator’s manual for the lawn mowers and on the oil canister, use the proportion indicated in the manual.

For a long time he did this. excess oil flowed from the engine onto the gas tank and carbon deposits constantly formed on the candle, since the manual indicated the proportion for the run-in engine 1:25, and on the canister. 1:50. After switching to a 1:50 ratio, the appearance of oil drips stopped. The candle continued to burn, but at a lower intensity (the carburetor was not yet adjusted).

Until now, some users of gasoline-powered tools determine the proportion of the fuel mixture “by eye”. If during the preparation of the mixture the amount of oil is underestimated, after a while an extraneous sound may appear immediately after starting the engine, which gradually disappears during warming up, and the engine stops with a sharp jerk. Continued use of the trimmer in this mode will lead to its failure.

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Fuel supply adjustment

Start slowly turning the fuel mixture adjustment screw until the engine starts to stall or stalls if you do not have time to catch the moment. After that, unscrew the screw a quarter of a turn if the engine has not stalled, or half a turn if it stalled. Start the stalled engine. Check by opening the throttle as the engine picks up speed. Continue to unscrew the screw No. 1 by a quarter of a turn until the engine starts to accelerate steadily during gas flow. This will be the moment of the most economical stable engine operation. For the PRORAB-8406 petrol trimmer, the adjusting screws are turned clockwise, unscrewed. counterclockwise, for some other brands the lawn mower can be the other way around.

Adjusting the carburetor lawn mowers, trimmer

Increased fuel consumption and the rapid formation of carbon deposits on the spark plug when using a properly prepared fuel mixture indicate the need to adjust the carburetor. Here’s how to adjust trims with carburettors with one fuel adjusting screw.

Flush the air filter before adjusting the carburetor. It is recommended to rinse it after every 10 hours of operation. After that, you can start adjusting. The photo shows the PRORAB-8406 petrol trimmer carburetor as an example. The numbers indicate the adjusting screws that we will use.

PRORAB-8406 petrol trimmer carburetor adjusting screws

Purpose of adjusting screws:

  • Fuel mixture adjustment screw.
  • Idling adjustment screw.
  • Maximum speed limiting screw.

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

Maximum speed limitation

After adjusting the fuel mixture and low speed, check how the lawn mower engine will run at maximum speed. If necessary, limit the maximum speed to the required level using the hollow screw. Loosen the locking nut and screw in the screw to decrease the maximum speed or turn it to increase. Tighten the nut after adjustment. Setting the maximum RPM is necessary to protect the trimmer motor from overheating and to be able to use the start key lock to reduce right hand fatigue.

In the future, it may be necessary to readjust the trimmer carburetor. For example, if the engine starts to rev poorly when running at full load, loosen screw another quarter turn. If starting is difficult, increase idle speed. Both weather conditions and the quality of the fuel mixture can affect the operation of lawn mowers. Vibration can cause the adjusting screws themselves to turn.

Spring may interfere

My first attempt to adjust the carburetor of the lawn mowers did not work, as the spring of the fuel adjustment screw interfered with. The factory spring turned out to be too thick in the compressed state and did not make it possible to reduce the fuel supply to the required level. I had to pick up another spring and continue adjusting after replacing it.

Fuel mixture adjusting screw with spring

In the photo above the factory spring, below the adjusting screw with the selected spring. I am writing about this because I’m not sure if this is an isolated case, and someone else may encounter the same situation.


“I bought a Stihl FS38 lawn mower for constant mowing of grass on an area of ​​about 10 acres. For 7 years of work, I felt how much easier it is to maintain the site with such equipment. The engine is quite economical, of course, its power is not enough for clearing bushes. Comfortable shoulder handle, comfortable to work “.

lawn mower Stihl FS38. Description of the model. Features of operation, maintenance. Model Description

the Stihl FS38 lawnmower is the lightest mobile version with 0.9 HP, it is designed for domestic use.

  • Thanks to the modern electronic ignition system, reliable starting and smooth operation of the engine is ensured.
  • Using the fuel pump, the operator has the ability, if necessary, to pump fuel into the carburetor.
  • Optimum maneuverability thanks to the D-handle, which makes the Stihl lawnmower comfortable to operate on difficult terrain.
  • All control levers are located on a special multifunctional handle (R), which ensures safe and reliable operation of the petrol trimmer.
  • Thanks to the AutoCut C5-2 mowing set, the cutting diameter is 380 mm.
  • The ergonomic shoulder strap allows you to hold the Stihl lawnmower on your shoulder, rationally coordinate movements during operation.
  • Low weight (4.1 kg.), Small dimensions, rational basic equipment. thanks to these characteristics, the STIHL 38 lawn mower is extremely comfortable to use.

Adjusting and repairing the carburetor lawn mowers

The trimmer does not belong to complex household appliances, therefore most of its breakdowns are mechanical in nature and are quite successfully eliminated with their own hands. Even if the engine fails for severe reasons. damage to the piston ring, for example, repairs are reduced to replacing a part.

And even with a relatively conventional design, such a part of the device as a carburetor needs adjustment.

Specifications and features

  • Mowing width: 23 cm;
  • Fuel tank capacity: 0.33 l;
  • Weight: 4.1 kg;
  • Bar: curved;
  • Line thickness: 2mm.

Thanks to the manual fuel pump, a person will easily be able to pump fuel into the carburetor. This point is especially important in a situation where the mower has been idle for a long time. Constantly adding fuel will allow you to quickly start the device even after a “long vacation”.

Together with the unit, the owner receives protective goggles and a mowing head in the complete set. You can understand the assembly features and other specific points of operation thanks to the manual presented on our website.

For other useful information, see the following document:

The curved boom of the STIHL FS 38 lawn mower with a rounded handle is worthy of attention. Thanks to this design, the device easily copes with cleaning the area even in narrow or confined spaces.

All controls are located on a comfortable handle, so it takes a long time to look for where and what to switch is not necessary. During work, such a moment is very important, because the operator can not be distracted and without unnecessary movements adjust the operation of the machine.

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. Lawn mower petrol carburetor adjustment. Mixing and feeding are adjusted appropriately depending on the tool and its mode of operation.

The device of the carburetor lawn mowers is the same for virtually all cases. Adjusting the carburetor of a Chinese lawn mower. It belongs to the category of float devices. The latter provide constant characteristics of the finished consistencies.

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The mechanism of the module is as follows.

  • Air enters the body of the air damper tube. Matrix lawn mower carburetor adjustment. The latter increases or decreases the air flow depending on its own position.
  • In the area where the hole for supplying gasoline is formed, the tube has a narrowing. a diffuser. Here the flow rate increases.
  • Fuel from the float chamber is fed into the tube through the nozzle. The float level determines the amount of fuel supplied. Because the pressure in the chamber is normal, and in the tube it is low due to the greater rarefaction of the air, gasoline is sucked through the nozzle.
  • The accelerated air flow picks up the fuel and atomizes it, forming an air-fuel mixture of a suitable density.
  • The mixture is sucked into the cylinder through the pipeline.

The more strongly the air damper in the tube is opened, the higher the density of the air flow, and, therefore, more fuel enters the cylinder. lawn mower stiga handle adjustment. Setting up the carburetor of lawn mowers is reduced to setting such a ratio of flaps at which the density of the fuel consistency becomes good.

Pros and cons of the model:

  • Excellent performance;
  • Compactness;
  • Low weight;
  • Functionality;
  • Endurance;
  • Possibility of self-adjustment of the elements;
  • The presence of a manual fuel pump;
  • D-handle, etc.

Naturally, the list of positive aspects should include the verification of the brand itself.

  • The need to constantly check the fuel level;
  • Small motor resource;
  • Low power;
  • High cost;
  • Lean equipment.

The presence of not particularly catastrophic shortcomings of the model does not have a negative effect on the popularity of the unit, because the ideal technique simply does not exist.

Lawn mowers carburetor device

The basis of the carburetor for lawn mowers is an aluminum body. It contains a diffuser (hole with internal contours). Air is blown through this hole. The flow rate of oxygen (air) depends on the cross section (orifice) of the diffuser.

The diffuser is equipped with fuel channels. Fuel is drawn in from them using the air flow.

Outside the carburetor is installed:

  • Fuel pump;
  • Jet system;
  • Air-fuel mixture control system;

Do-it-yourself lawn mowers carburetor adjustment

A lawn mower 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.

Mesh filter. There are often only two problems with this element:

  • Blockage.
  • Breaking.

In order to find out the cause of the breakdown, the fuel filter cap is unscrewed to remove the strainer. If dirt simply accumulates on it, then flushing in gasoline or blowing will help.

If there is visible damage to the mesh filter, it is imperative to install a new one. There may also be damage to the fuel supply pipe (during repair, they practice checking this element).

Blowing out carburetor parts with compressed air is an acceptable and convenient repair practice.

The principle of operation of the carburetor lawn mowers

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 union 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.

Phased operation of the device:

  • 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 pressure drop, the fuel penetrates through the jet.
  • 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.

Simply put, adjusting the carburetor on a lawn mower is about creating an optimal fuel mixture through correct air supply.

How to adjust the carburetor on a lawn mower

Before adjustment, you must thoroughly clean the filters according to the maintenance in the instructions.

Further adjustment of the carburetor of the lawn mowers with their own hands is carried out with the adjusting screws. There are three of them:

  • Right;
  • Left;
  • Lower.

Right (L). adjusting the fuel mixture for low rpm.

You need to find the maximum idle speed. To do this, slowly unscrew the screw (L) to the right and left.

To adjust, turn the screw a quarter turn counterclockwise.

Lower (T). responsible for adjusting the engine at idle.

  • Clockwise. increase;
  • Counterclockwise. decrease.

For the correct adjustment of the idle speed, it is characteristic:

  • Stable operation of a cold engine;
  • Not overestimated speed of a hot engine;
  • Large headroom for the trimmer head;
  • Stable operation of the engine when changing position (sharp lifting or lowering of the knife).

Left (H). mixture adjustment at high rpm. (The screw is adjusted last).

The carburetor setting for lawn mowers with the last screw is done as follows:

  • Open the throttle to full, while at the same time give full throttle. Turn the screw clockwise until the revolutions fall (in this case, orientate by ear).
  • Turn the screw counterclockwise as slowly as possible until the engine runs unevenly.
  • Then turn back quite a bit, barely hearing a stable, even operation.
  • For a more visual use of skills, it is more convenient to consider the work of an experienced user:

Interestingly, from the point of view of the author. The setting (its correctness) is determined by the color of the spark plug, and not only by engine speed and stability.

Correct adjustment of the carburetor with your own hands in this case. combustion of the fuel mixture without residue, the color of the candle should be light brown.