How to adjust the carburetor of a Shtil 180 chainsaw with your own hands: step-by-step instructions, materials and tools

High-speed gasoline engines installed on Shtil chainsaws require constant attention and periodic adjustment. Otherwise, achieving stable operation of the motor will not be easy. The company's engineers tried to make the carburetor adjustment screws of the Stihl chainsaw as convenient as possible. Therefore, it is possible to configure the operation of the motor even for an inexperienced user.

Design and principle of operation of the Shtil 180 carburetor

Most of the components and parts of the Stihl chainsaw are made in China. The quality of the engine has decreased somewhat, but not particularly critical. Some of the most important components, such as carburetors, continue to be produced in Europe. Therefore, on sale you can find Stihl chainsaws with “native” carburetors, as well as with the Chinese version.

On the original SHTIL MS 180 carburetor, the adjustment screws rotate quite accurately throughout the life of the chainsaw. At first, the Chinese adjustment screws also look quite decent; you can adjust the operation of the chainsaw to an acceptable level of fuel consumption, without failures in operation. But the quality of the membrane is lower, so adjusting the carburetor of the Stihl chainsaw may not always be stable.

The original Shtil 180 device uses a replica of the successful Japanese ZAMA model. It is clear that in Chinese Calm the design of a chainsaw carburetor is already a copy of a copy.

ZAMA is one of the most reliable and economical in its segment. This means that there is nothing complicated in adjusting the carburetor with screws. Like any other Japanese technology, it is quite easy to set up. The worker will only need to be careful when rotating the adjustment screws with his own hands and a thoughtful approach to selecting the operating mode of the chainsaw.

How ZAMA works - the pump lifts gasoline from the tank, throws it through the channel into the main chamber and then into the diffuser. The pressure generated by the pump forces the fuel through the jet or injector into the air stream, which is drawn by the piston through the carburetor.

In theory, if the fuel and air consumption are correctly selected, then this is enough for the chainsaw to work, and quite steadily, but at the same speed and without load. The Shtil 180 model is distinguished by a minimum number of transient processes, so it starts well and maintains stable speed even when cold.

In addition to the pump, diffuser, jet, nozzle, the carburetor uses auxiliary elements:

• control membrane with rocker arm and valve;
• needle valve;
• throttle and air valve.

The position of the elements is set with screws. They are needed to regulate the mixing of air with gasoline, control the operation of the Shtil at different speeds, at different air-fuel temperatures. A simple increase in air or gasoline consumption would cause the chainsaw to stop.

Fuel pump

The main element of the carburetor is the fuel supply pump. In Shtil it is of membrane type. This is both good and bad at the same time. The membrane provides a more uniform supply of gasoline than a spring rod, but is gradually destroyed by fuel vapor.

To drive the membrane, a channel is used that connects it to the chainsaw engine crankcase. Every time the piston rises up and down, a vacuum is created inside the crankcase, which is transmitted through the channel to the membrane, causing it to move. In one cycle, the membrane rises, sucks gasoline from the tank (through the valve), and then, lowering, pushes it further along the channel in the carburetor body.

Distribution chamber

The main chamber, also known as the distribution chamber, accumulates gasoline in the carburetor. But further supply to the nozzle (diffuser) occurs under the control of another membrane element connected to the rocker arm. The latter can raise and lower the needle valve. The adjustments of this chain (membrane-rocker arm-valve needle) determine the gasoline consumption in the carburetor and determine the stability and response of the chainsaw under load. And also the efficiency of Stihl’s work.

The membrane moves due to the vacuum created by the air flow in the carburetor diffuser. The higher the air speed (the stronger the vacuum), the higher the membrane raises the valve needle, and more fuel is released into the injector. This automatically adjusts the air-gasoline ratio or mixture quality.

Some chainsaw models have two screws for adjusting the mixture quality. With their help, you can adjust the cross-section of the channel from the membrane to the nozzle. This improves engine efficiency. Shtil has 180 individual adjustment screws. It is believed that additional screws are not necessary. Instead, a flow adjustment screw is used on the jet, which is responsible for the idle speed of the Stihl.

This control scheme is considered more resistant to channel contamination.On the one hand, fewer adjustment points significantly reduce the ability to fine-tune the chainsaw. On the other hand, when working with Shtil, it is better to turn one adjustment screw than two, even at the expense of accuracy. Although in reality the point is probably to make the engine more stable.

Nozzle

Responsible for atomizing fuel in the carburetor diffuser. Equipped with a check valve to prevent gasoline from accidentally leaking back into the chamber.

When assembling the Shtil, before installation, the check valve is tested for gasoline leakage, and sometimes adjusted according to the flow section. When Stihl is stored for a long time, the mixture of gasoline and oil often turns sour in the valve, so before adjusting it is necessary to blow out or rinse the channels with clean gasoline.

In addition to the injector, the idle jet (sometimes jets) “look” into the air channel. It works with the throttle valve closed (the gas on the chainsaw is completely removed) in idle mode. The working cross section is smaller than that of the nozzle, so it has virtually no effect on the main mode. Adjusting the idle speed screw on the Stihl is considered one of the most important and will require enormous patience.

Throttle valve

Installed in the flow part. It looks like a round plate on a rotating axis. Needed to regulate gasoline flow through the nozzle. When the channel is partially blocked by the throttle valve, the air speed increases sharply, the vacuum increases and so does the amount of gasoline sprayed into the diffuser by the nozzle.

It is possible to adjust the damper position at minimum and maximum with a screw.

Air damper

Used to quickly deplete the fuel mixture after starting Calm.The adjustment of the damper position is such that when the chainsaw starts, the channel cross-section is blocked. The amount of air at the start must be reduced to enrich the mixture with gasoline vapor.

After starting, the damper rotates parallel to the air flow without creating resistance. The same damper adjustment scheme is used if it is necessary to ventilate the Stihl engine after an unsuccessful start attempt.

There are no other ways to remove excess gasoline from a chainsaw cylinder.

Main types of faults

Most of the difficulties in working with Stil are related to basic problems:

• difficulty starting the chainsaw;
• unstable operation at idle and in operating mode;
• gasoline is lost or there is clearly not enough fuel supplied.

Sometimes, after a dozen manipulations with the adjustment screws, the Stihl carburetor begins to overflow. It may be necessary to remove the fuel pump.

Chainsaw won't start

Even a fairly worn Shtil, with already reduced compression, should start without additional adjustments. On a cold engine, you need to pull the starter cord a couple of times to blow out everything remaining in the cylinder. Next, close the damper, turn on the power to the spark plug and strongly spin the flywheel. Calm always starts confidently, without intermediate jerks.

If the Shtil does not start, it means that either the mixture is not supplied to the cylinder from the carburetor, or the spark plug is filled with gasoline. In the first case, the membrane or injector valve is to blame. Disassembly is required, the membrane needs to be changed, the valve must be washed to remove any remaining engine oil. After assembly, you will have to adjust the carburetor speed at idle.

Sometimes, due to dirty gasoline, the filter mesh simply sticks; no adjustments are needed, just unscrew the screw, wash the mesh, put it back in place and try to start the Shtil again.

Like in the video:

RPM fluctuates at idle

Even when cold, the Stihl starts up and runs quite steadily, first at high speeds, then goes to idle. The speed may fluctuate if the engine is not warmed up enough. The problem is usually with the supply - it is clearly not enough for stable operation.

The first step is to unscrew the screw on the cover and check the filter between the fuel pump and the valve with the needle. It is possible to blow air through the channel, but be careful not to damage the pump membrane.

The next step is to check the jet. At idle, you can turn the adjustment screw. The motor should respond by changing the speed. If nothing happens, there is no reaction to the rotation of the screw, then the nozzle will need to be cleaned.

The scheme is something like this:

1. Unscrew the screws and get to the jet.
2. Blown with compressed air from a compressor.
3. For a day, the jet is placed in a jar of acetone. Alcohol, gasoline, kerosene, and solvents are not suitable.
4. After 24 hours, take out the nozzle, and use a sharpened wooden toothpick to make a hole. Metal cannot be used otherwise the saw’s carburetor will be sent for repair.

Can be installed on a carburetor. After cleaning, you will have to work the idle speed screw to adjust the lower speed level on the Stihl.

Loss of power, high gas consumption

Another problem is that the carburetor overflows, despite the fact that the adjustment screw is fully tightened. As a result, fuel consumption almost doubles, in addition, Shtil gets very hot and loses power. Even with the choke fully open.

The chainsaw cannot be operated in this mode. Despite the protective coating, the piston may burn out. The life of the candle is reduced by almost half. In addition, overheating often causes deformation of the gaskets and carburetor support surface. A side air leak appears through the gasket. Now, even if you adjust the screw to increase the speed, you will not be able to increase the power of the chainsaw.

The cause, as a rule, is a damaged pump membrane. If the carburetor is Chinese (with the inscription “China” on the body), then it definitely needs to be changed. After a year or two of operation, it will still become limp under the influence of fuel. We need to look for the owners of the original Shtil. The repair kit usually contains a spare membrane, so it needs to be installed instead of the Chinese one. At the same time, check for air leaks through the gasket.

The spark plug will need to be cleaned of carbon deposits using the same procedure as the jets. Cleaning the electrodes is allowed after soaking in acetone (nail polish remover) only with a wooden sliver. You can't burn it.

Also, after overheating, you need to check the operation of the adjustment screws. Sometimes they burn into the threads of the body material.

Adjusting the carburetor of the Shtil 180 chainsaw

On the case you can find three screws - “L”, “S” and “H”. This is not difficult, since all the adjusting screws on the carburetor are marked. The upper and lower speed ceilings are set first and last; their position directly affects the operation of the jet. Screw “S” is used when adjusting the carburetor to adjust the XX.

Next, using a flat-head screwdriver, you need to screw all three until they stop, but with minimal tightening force. To start the chainsaw, turn “L”, “S” and “H” one and a half to two turns.

Important! The saw can be adjusted only after the engine has warmed up.

After starting, at least 5 minutes must pass, after which you can adjust the idle speed. First, by rotating the “S” screw with a screwdriver half a turn left and right, find its position at which the idle speed will be maximum. It must be remembered that the mixture formation system does not immediately respond to changes in flow rate, so turns with a screwdriver must be done quite slowly.

After determining the maximum, all that remains is to tighten the screw “S” ¼ turn.

After adjustment, you need to run the saw under a full heat load and check the operation again at idle.

Adjusting the carburetor of a Stihl chainsaw using adjustment screws is not as difficult as you can read in the instructions. The only condition is that you need to use high-quality fuel - A92 with the addition of 5% Stihl branded two-stroke oil.

Tell us about your experience in operating and setting up Stihl chain saws - what features should you pay attention to when setting up the carburetor?