STIHL fs 250 carburetor adjustment. How to properly tune a Chinese-made saw – adjusting instructions

STIHL grass trimmer fs 45 instruction manual. STIHL FS45 lawnmower

When discussing the design and performance of the world famous manufacturer’s products, special attention should be paid to its main competitive advantages. The advantages of STIHL gasoline grass trimmers, in comparison with electric models, include:

  • Dependence of the device performance solely on the availability and amount of fuel;
  • Relatively low weight of the grass trimmer;
  • the maximum simplicity of the device and operation;
  • adaptation of the power unit for mowing, including thickets;
  • economy;
  • maneuverability and functionality.

Naturally, it is not without obvious disadvantages, the list of which includes:

  • The fuel mix must be prepared in the recommended proportions;
  • risk of engine failure due to low-quality fuel;
  • the need for regular maintenance;
  • High noise level.

Among other things, when comparing gasoline and electrified trimmers, you should consider the presence of an electric motor in the latter. Only operate these machines if you have access to a power outlet.

When adjustment of the carburetor is necessary?

Stable operation of the brushcutter carburetor depends to a large extent on its correct setting.

Adjustment of the assembly is required in the following cases:

  • after the new grass trimmer has been run-in, when 4-5 full tanks of fuel have been used during operation;
  • When the operator frequently changes the brand of gasoline used for refueling;
  • Sudden changes in the weather;
  • Due to prolonged storage of the grass trimmer;
  • as a result of the regulating bolts of the brushcutter being unintentionally unscrewed, caused by strong vibration of the brushcutter motor;
  • because of the dramatic increase in the amount of fuel consumed by the trimmer.

Adjust the carburetor mower also need in those cases where the spark plug tool quickly appears on the ignition, as well as a sharp increase in the volume of exhaust emissions trimmer.

The carburetor on your lawnmower

The carburetor for lawnmowers is based on an aluminum housing. It has a diffuser (orifice with internal circuits). The air is forced in through this port. The flow rate of oxygen (air) depends on the size of the nozzle.

The diffuser is equipped with fuel channels. Fuel is sucked out of it with the help of air flow.

Construction of the carburetor

In Fig. Model No. 1 shows a modern carburetor for a German-made STIHL 250 chain saw. It is a unit the size of half a human fist. The mechanism is made by Walbro, Taiwan. Casing material: rustproof steel alloy. At the bottom of the device is fixed flap, which provides an even flow of fuel-air mixture to the engine combustion chamber.

These are the holes for attaching the assembly to the power train housing. Between the flanges of the mixture and the engine combustion chamber is a sealing gasket. The booster pump is located under the throttle rod. It has a small piston with a rubber ring.

There are a number of user-friendly spring-loaded adjusting screws on the front of the housing:

STIHL chain saw carburetors can be adjusted with these screws.

A major innovation with the STIHL 250 chain saw carburetor is the heating system. To prevent the mechanism from freezing during winter operation, it has a special system that preheats the steel housing during operation. To do this, the machine is set for winter operation.

The housing is blown by heated air sucked from the engine. This mode of operation prevents icing on, freezing of the nozzles and provides a normal supply of the air-fuel mixture. When switching to summer mode the hot air damper is closed. Summer mode is characterized by natural cooling of the machine.

What you need to set up

Before adjusting the THR it is necessary to make sure that both filters (air and fuel) are clean. Also, there must be no air sucked in from the side of the engine (through packings, gaskets under the UPT or its booster pump or wherever), otherwise you won’t be able to tune the carburetor.

Practically any carburetor is adjusted with 3 screws:

  • 1. The main jig screw, marked “H”, which is used for setting the maximum rpm of the saw motor.
  • 2. Idle speed nozzle bolt designated “L” and used for adjustment of low revolutions. That is, for adjusting the idle speed.
  • 3. The idle speed adjustment bolt, designated at various. “LA” (STIHL), “T” (Partner, Husqvarna).

There are also carburetors with fewer adjustment screws. This is the way manufacturers try to protect their products from unprofessional interference and at the same time they try to simplify their setting.

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For safe adjustments, the rules must be followed during the adjustment:

  • 1. the tool must be placed on a level surface of a rigidly fixed object (workbench, shelf, table).
  • 2. The chain should be directed away from yourself and others present.
  • 3. A safety distance must be kept between the chain and any surrounding objects to ensure that they cannot come into contact with each other.

In such cases, you can adjust the carburetor on your chainsaw as follows. First we start the tool and warm it up for 10 minutes.

Begin the adjustment of the UUT by finding the position of the adjusting screw “L” which gives the best idle speed. To do this turn this bolt very slowly and smoothly to one side and back to the other. Repeat this several times until the desired position is found. Then turn the “L” screw 1/8-1/4 turn (see the machine documentation for the required value) anticlockwise.

Then continue adjusting the idle speed with the screw “S” (“LA”, “T”):

  • If the chain after manipulating the “L” bolt is stationary, then turn the “S” (“LA”, “T”) clockwise smoothly until it starts to move. Then turn back the “S” 1/8-1/4 turn.
  • If the chain is still moving, turn the S (LA, T) of the VASP until it stops, then turn the S 1/8-1/4 turn in the same direction.

The engine should run smoothly. And check it to see how it accelerates. The engine is considered to work normally in an acceleration mode if the rpm rises to its maximum value in a short time and without “slack” when the gas pedal is depressed gently. If the engine does not run evenly and/or accelerates poorly, turn the L-STOP switch slightly, no more than 1/8 of a full turn.

Now check the setting of the adjusting bolt “H”. To do this, rev the engine up to maximum rpm. Only you shouldn’t drive it like that without load for a long time, you should make pauses. Look at the exhaust and listen to the engine. If there is a lot of smoke coming out of the muffler and the chain saw is making a lot of noise, the carburetor is mixing too much.

When the chainsaw makes a squealing sound, the engine gets very hot, the exhaust is accompanied by a crackling sound and/or the ignition falters, that is detonation. the mixture is too lean and the maximum engine rpm is higher than it should be. This causes overheating of the power unit, piston burnout, rapid cylinder wear and spark plug burnout. In this case it is necessary to turn “H” 1/4 turn of the VAR.

To finish the adjustment, check the saw at idle speed. If the UUT is correctly adjusted it should work like this:

stihl, carburetor, adjustment, properly, tune, chinese-made
  • 1. The chain is stationary.
  • 2. Engine sounds almost like a four-stroke.
  • 3. When the gas pedal is depressed the maximum rpm will be reached quickly.

If these conditions are not fully satisfied, you should use “S” (“LA”, “T”) as indicated above or repeat the setting from the beginning.

This is the approximate setting. You need a tachometer to be precise. Do all the same, but turn the adjustment screws according to the readings of this device. This will allow you to accurately and most likely with the first time to adjust the carburetor, achieving, depending on the model of woodworking tool to set the idle speed of 2800-3300 rpm or higher and the maximum. 11000-15000 rpm. How exactly it should be set is in the technical documentation (instruction manual) of the saw.

After maintenance, such as disassembly and washing or previous unsuccessful attempts to adjust this assembly may be completely unadjusted. So much so that the saw will not start at all. In this case it is necessary to tune the engine power supply system in 2 steps, conventionally called:

At the first stage we slowly screw in the adjusting screws “L” and “H” up to the stop. You don’t have to put a lot of effort and try to tighten them. Then turn both screws back for many models by 1 turn. And for some, 1.5 turns. There may be other attitudes. You should check this in technical documentation of your chainsaw. At a number of models a tip is put directly on a cover of their case near adjusting screws.

This is the factory recommended basic setting for the carburetor. Do not turn the S screw (LA, T) in any way unless you have already turned it. When it is already torqued, you have to work with it as well. Slowly screw in the “S” of the VFD as far as it will go.

Why the Grass Trimmer Is Not Receiving Gasoline

Go to the final stage. Trying to start the engine. If you have not manipulated the “S” (LA, T) and “L” and “H” have been set exactly as recommended, it should start.

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If you had to tighten the “S” setting for the above mentioned reasons, it is most likely that you would not start the engine immediately. You will have to tighten this screw after each attempt to turn it by 1/4 turn and try to start the engine again. Eventually it should start.

Then warm up the engine for 10 minutes. If after the engine start or during the warm-up it is not stable or the chain starts to move, slowly and carefully turn the “S” (LA, T) of the VFD. As soon as the engine starts to run steadily and/or the chain stops, immediately stop the adjustment. If the engine stalls, then turn this screw for 1/8-1/4 turn (see the datasheet) of the PSA.

Problems and solutions. repair with your own hands

But what to do if suddenly the breakdown of the mechanism could not be avoided? We won’t puzzle out the reasons, but it won’t be superfluous to consider possible problems that may arise with the mower, as well as methods of their elimination by your own forces.

stihl, carburetor, adjustment, properly, tune, chinese-made

The engine doesn’t start. If you are faced with this problem, then initially you need to assess the amount of fuel in the fuel tank, maybe the problem is not as such, and you only need to add fuel and continue working. By the way, you should pay special attention to the fuel used, because the lifetime and quality of the mower depends on its quality. Specialists recommend gasoline AI-92, not lower.

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Another possible cause of the mower’s irregular running may be a dirty fuel filter. It should be inspected carefully, cleaned if necessary. If the filter cannot be repaired yourself, you should replace it with a new one.

Do not forget about the air filter, clogging which can also lead to tool failure. To avoid this, the part is removed and washed in water and detergents, or in gasoline if you do not have access to water supply.

Then the filter should be thoroughly rinsed and dried, paying close attention to the structural integrity. Before installing the part in the mower, lubricate it with a small amount of oil. However, if you do not want to bother with cleaning the unit, then we suggest you familiarize yourself with a lawn mower with mulching function, because it will not only mow the lawn, but also prepare a further fertilizer.

The spark plug can also affect the performance of the engine. It is necessary to unscrew it and check its condition, if necessary, replace it with a new one.

If after all these manipulations, the engine still does not start, then you can resort to the tips of experienced masters, who used them in practice.

You need to adjust the speed with the carburetor screw. Place the mower in such a way that fuel hits the bottom of the carburettor. To do this, the tool is placed so that the air filter is on top.

Next, you need to remove it and pour some fuel into the carburetor, then install all the parts in place. The engine should start.

These tips are not a panacea, but they are quite effective and useful.

Mower stops shortly after starting. The main reason for this is that the carburettor is not properly adjusted. It is easy to identify the problem, you will feel a strong vibration during mower operation. To correct the problem yourself, you can look at the instruction, which describes the problem in detail and methods of elimination.

Pay extra attention to the fuel line. it is often the reason for the tool stalling. Check and clean it often.

Smaller parts like the cable or the fuel intake hose can interfere with the stability of the machine. That’s why it is important to keep an eye on them for cracks and minor punctures.

stihl, carburetor, adjustment, properly, tune, chinese-made

Many people may be put off by the relatively high price of STIHL products, but when you think about it, it’s more important to have reliability and good performance or to cut corners on quality? But if you set out to save money, then we offer you the option of lawn mower with your own hands, collecting the device with your own efforts you will know all the nuances and the structure of the tool.

Of course, you can choose a cheaper Chinese analogues, but then no one can vouch for the result of the final work and for the service life, which is very short in such models. It’s better to buy a STIHL mower from a reputable company and then get many years of stable work.

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Adjustment process

The basic setting

The basic adjustment of the chainsaw carburetor is done during the factory test. During the machine tuning the screws H and L should be set to H=L=1.25 turn.

During the first 3-4 hours of operation the machine is adjusted to a richer fuel. To do this, the engine speed is reduced by 600-700 less than the maximum allowable.

The maximum allowable number of engine revolutions depends on the chainsaw carburetor. For most chainsaws these figures are: in working mode. 12500 rpm, in idle mode. 2500 rpm.

The shaft speed should be measured with a tachograph. In the absence of such a device set bolt H in the direction of fuel mixture enrichment in relation to the initial position.

Fine tuning

For fine tuning, turn all screws one after the other. Make fine adjustments until the maximum permissible engine speed is reached.

Adjustment of the low speeds by turning the bolt H in different directions. Then the position with the maximum shaft speed is determined. From this position turn the bolt 1.25 turns counterclockwise.

While the chain is moving along the bar, turn screw T counterclockwise until the chain comes to a complete standstill.

Exact adjustment of the carburetor is carried out with the chain saw running. During operation turn bolt T until the chain moves. Then turn it in the opposite direction until the chain stops.

Precise adjustment of high engine rpm is done by turning the screw. Noises are eliminated at maximum speed. Turn the L screw 1.25 turns in different directions to find out.

The tool whistles when the lean mixture is delivered. If the mixture is too rich, you will get more exhaust fumes. No annoying whistling if the machine is correctly adjusted. The chain is at a standstill when idling.

Setting the L-Bolt to lean fuel makes it hard to start the chain saw. Setting bolt H to “poor” fuel results in loss of power. Setting both propellers to “rich” fuel causes significant shaft speed loss.

Troubleshooting and repair

STIHL 180 chain saw carburetors need initial adjustment and periodic adjustment. You can tell if it’s needed by looking at the following signs:

  • Engine trouble, such as the engine not starting or stalling immediately after starting. The most common cause is the use of a low-quality fuel mixture.
  • Fuel consumption and increased emission. Exhaust becomes higher due to incomplete combustion. This problem is most commonly caused by an excessive level of fuel.

Other malfunctions may also occur, such as clogging due to a damaged air filter or scale formation. The causes may be due to gasoline remaining in the fuel tank when idling for a long period of time. This is due to the fact that the fuel is exhausted, which spoils the device.

Regardless of the cause, the carburetor will need repair, which is most often reduced to adjustment. The way to do this depends on the model of the chainsaw, but it is possible to follow the general principles.

How to remove the carburetor from a chainsaw

Remove the carburetor from the STIHL chain saw before adjusting. To do this:

  • Turn the catch to the left to remove the cap.
  • Remove the filter by unscrewing the two nuts that hold it. Special screwdrivers with matching bits are recommended for easier use.
  • Remove all the rods, including the carburetor lever.
  • Remove the carburetor and then disconnect the fuel hose.

It is recommended that you memorize the location of the parts so that you can then put the carburetor in place and no unnecessary fasteners or warps and slots are left.

How to clean

If the chainsaw stalls when idling, it is necessary to disassemble the part and clean it. This is especially important for cleaning the additional filter. This detail is a mesh. To get to it, you need

Remove the largest cover. Remove the diaphragm located under the cover. Clean the mesh that is located in the recess

Be very careful when doing this because the mesh might fall out. Use a copper wire for cleaning

Additionally, all passages should be flushed and blown. The last procedure is necessary if the carburetor does not receive gasoline.

How to set up

Adjusting the carburetor on a STIHL 180 chain saw is important for both improving performance and saving fuel.

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