Chainsaw carburetor adjustment. Characteristics of chainsaw settings

When and why you need to adjust the carburetor

A chainsaw is a tool equipped with a two-stroke engine, the carburetor of which requires adjustment from time to time for normal operation. The standard or factory setting and adjustment of the chainsaw carburetor is performed at the factory during the tool assembly process. However, for stable operation and good performance, it is necessary to adjust the chainsaw carburetor even during break-in.

After and during the break-in process, it is the owner’s responsibility to properly tune the carburetor for the most efficient, safest, and most durable operation of the chainsaw engine.

Do-it-yourself chainsaw carburetor adjustment – video on the example of a Husqvarna saw:

The main reasons that require adjustment of the chainsaw carburetor:

• Gasoline consumption has increased, the device consumes too much oil;
• During operation, the chainsaw gets very hot, smokes, makes popping or explosive noises (such a problem is a signal that you need to clean the muffler, blow the breather and rinse the nozzles in acetone).
• The engine stopped idling;
• The chainsaw begins to stall after some time after work, in general, the tool began to work worse – it does not develop power so effectively, does not develop maximum speed;
• The chainsaw vibrates heavily during operation;
• It is also necessary to adjust the carburetor if the chainsaw has previously worked on poor-quality fuel or an improperly prepared fuel mixture.

Chainsaw carburetor setting:

What tool is needed to adjust the carburetor?

The following tools are used to set up and adjust the carburetor:

• Tachometer (a special device for adjusting the carburetor, with the help of which the owner of the chainsaw can determine the maximum engine speed for this model, and then correct it according to the manufacturer’s recommendations);
• Adjusting Wrench (a special tool, often only available in service centers, is not supplied with chainsaws as it can be used by inexperienced users, resulting in breakage of the chainsaw rather than adjustment).

Note: the setup and adjustment of the carburetor of a chainsaw of any model, as well as its repair, should be carried out only by service center specialists, while the tool is under warranty.

Independent attempts to clean the carburetor, flush it and eliminate existing malfunctions may not give the desired result.

Overview of tools for regulating the operation and repair of a chainsaw carburetor:

Theory and principles of operation of the fuel system, carburetor design

How the carburetor works

In different models of chainsaws, the structural design of the carburetor may differ, but the principle of operation of this part is always the same: the forced air flow moves in the direction of the air duct (impulse duct), the air is regulated by an air damper. When entering the impulse channel, the air changes its speed. The speed change is effected by a special valve that closes the air intake. Fuel is supplied to the air duct, which is mixed with the air flow. This creates a combustible fuel-air mixture, which then enters the engine and burns there.

Figure 1. Scheme of the principle of operation of the chainsaw carburetor

Scheme of the principle of operation of a chainsaw carburetor

Figure 2. Husqvarna 137 chainsaw carburetor

Husqvarna 137 Chainsaw Vergaser

Figure 3. The principle of operation of the fuel system using the example of a two-stroke chainsaw carburetor

The principle of operation of the fuel system using the example of a chainsaw carburetor with a two-stroke engine

The main task of the carburetor is the continuous and high-quality functioning of the engine.

The components of a carburetor are:

• Aluminum housing (solid, cast);
• Jets or valves that regulate the amount of fuel entering the carburetor;
• Flood chamber;
• Diffuser;
• Spray.

On figure 1 you can see the location of the key components of the carburetor, and on figure 2 you can see the appearance of the chainsaw carburetor. In order to properly tune the carburetor, the chainsaw owner should know how this part works:

• When the engine starts, the air damper opens;
• Due to the piston stroke, rarefied air is formed in the float chamber and air passage;
• Then the air mass is drawn in through the diffuser where it mixes with the fuel that has also entered the float chamber through the fitting, creating a fuel-air mixture that enters the intake ports.
• The last stage is the entry of the mixture into the combustion chamber of the engine.

By adjusting the position of the damper, the chainsaw owner can either add air to the fuel or lean it – meaning the fuel mixture enters the combustion chamber faster or slower. Carburetor adjustment screws are used to adjust the engine speed. An air filter is installed above the carburetor, which cleans the air before it enters the air duct.

Video showing the Husqvarna chainsaw carburetor adjustment chart:

Figure 4. Table of proportions of oil-fuel mixture for Husqvarna chainsaws

Table of proportions of oil-fuel mixture for Husqvarna chainsaws

The carburetor arrangement of expensive and medium-priced chainsaws is almost identical. Cheap China chainsaws often differ from expensive original chainsaw models in that they are missing some parts in the carburetor assembly. About the features of adjusting the carburetor of Chinese chainsaws, you can read later in this article.

Step-by-step sequence of the setting process

Before proceeding with the setup, remember:

• The setting is only “hot”, that is, the engine must be started and warmed up for 10 minutes.
• Then the adjusting screw is turned counterclockwise and the chainsaw chain is stopped;
• Before adjusting, the chainsaw must be placed on a flat surface, and the saw part should be directed away from the owner.
• Three screws with letters are used for adjustment, H – controls the upper speed, controls the main jet, L – controls the operation of the idle jet, controls the low speed, T – controls the idle speed.

Carburetor adjustment step by step:

• Turn the L screw left to right or right to left, find the maximum engine speed, and then back off 1/4 turn;
• Do the same with screw H;
• The chainsaw should run for a few seconds, use a tachometer to determine the maximum engine speed – their number should not exceed the maximum specified in the instructions for the chainsaw;
• If the chain idles, turn the screw T in the direction of chain movement until the chain stops completely (idle is only ever adjusted by screw T turning from right to left – counterclockwise – until the chain stops completely).

When the carburetor is properly adjusted, the engine spins quickly, the engine sound is clear and rhythmic, the chain does not move at idle.

Why can regulation be ineffective?

• The screw connections are loosened, air penetrates through the resulting gap;
• The nozzles are clogged with resinous deposits, rinsing with acetone is required;
• Ignition not set.

Features of the device of Chinese chainsaws

Chinese chainsaws, especially new models, may have some carburetor adjustments. Here are the main features:

• To adjust the carburetor on a Chinese chainsaw, you must first adjust the idle mode so that the chain does not move along the tire.
• In medium speed mode, there may be a smoky exhaust, which is removed by turning the lean mixture screw.
• Do not exceed the chainsaw motor’s maximum RPM (use a tachometer);
• If you correctly set the carburetor on a Chinese chainsaw, and the gas is reduced to a minimum, the device will not stall, and it will also quickly develop speed.

Video about adjusting the carburetor on a Chinese chainsaw

Chainsaw carburetor adjustment and tuning video

Owner Feedback

Gena, Smila:

I work with an ordinary China saw, it runs for me for about ten minutes from a cold start, then it starts to falter. The candle is dry. Time elapses when full throttle is pressed, the saw starts and again for 10 minutes. In general, I changed the carburetor in the service, and filters and candles did not help. And this is what helped me: I set the spark gap with a tri-fold printer sheet, not a probe. It turned out that the problem was in the ignition, not the carburetor

Leonid, Poltava:

I want to share the problem and its solution, maybe someone who had the same problem will be interested. I bought a Chinese chainsaw, it works great, starts and idles. When I start the saw it runs fine for the first 30 minutes, after 20 minutes it heats up and revs up sharply, then it stalls and won’t start again until it cools down. The problem was solved simply, the carburetor needle stuck, it turned out after tuning in the SC

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