How To Adjust Fuel Supply On A Chainsaw

how to adjust the fuel supply on a chainsaw

  • 1 carburetor device
  • 2 Other faults
  • 2.1 Water in gasoline
  • 3 Candle Check
  • 3.1 Checking power supply
  • 4 Adjust the carburetor
  • 5 Setting the carburetor on a warm engine
  • 6 videos

A chainsaw is the tool that many owners of private houses prefer to have on hand, because you can not do without it during the installation of wooden structures, repairs, and also if it is a simple cut of a branch or a whole tree. The advantage of the chainsaw is that it does not require an electrical network and extension cords that extend throughout the house and yard, however, this tool must be refueled with gasoline mixed with oil as necessary.

Having several advantages over an electric saw, a chainsaw can present to its owner at the beginning of work or in the process several unpleasant "surprises" associated with the fact that:

  • the tool suddenly refuses to start;
  • motor saws begin to work with terrible interruptions;
  • the motor simply stalls during operation;
  • motor power does not reach the desired value;
  • strong smoke appears during operation of the tool caused by certain malfunctions.

The solution to all these problems is often one. just figure out how to adjust the carburetor on a chainsaw and in which cases it needs to be done.

Carburetor device

To understand how to properly adjust the carburetor of a chainsaw, you need to understand how it works. In the diagram below, you can see how this device works.

Simplified carburetor circuit

Consider the principle by which the main dosing system works.

Different pressure is generated from below (1) and in the upper part of the membrane (2), as a result of which the diaphragm with a cylindrical piston (3) is activated and it begins to rise. The process continues until the engine accelerates. This effect is achieved due to the fact that, by opening the throttle (5), the engine, increasing the speed, creates a certain vacuum, and the diaphragm together with the cylinder piston (3) rises with the needle (4). Due to this, the amount of fuel entering the engine increases. This whole system stabilizes the vacuum in the needle area, so the fuel mixes better with air.

The principle of operation of chainsaw carburetors of different manufacturers is the same, but the device may vary slightly.

After examining the illustration, you can find out what the carburetor parts are called.

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Disassembled carburetor

Table with names

Other malfunctions

Chainsaw won’t start

Before undertaking carburetor adjustment, you need to find out the cause of a possible malfunction. Consider situations that may arise:


It is quite clear that before you do something with a chainsaw, you need to understand why it does not work well.

First you need to take care of a convenient place where you can do adjustments or repair the carburetor. This should be a flat area wide enough so that the parts laid on it are not lost when falling to the floor.

There is water in gasoline

Water in gasoline

Compared to water, gasoline has a lower density, as a result of which it will always be above the water that has entered the tank. A chainsaw will not be able to work on such a composition, so you need to get rid of what should not be in the tank by draining water from it.

To check whether this is so, you need to disconnect the fuel pipe from the carburetor and insert it into a plastic bottle and pour gasoline into it. As you can see in the photo. it will gather below. In this case, the carburetor must be disassembled and cleaned. If there was no water in the fuel, then we return it to the tank and look for another malfunction.

Video: How To Adjust Fuel Supply On A Chainsaw

The properties of gasoline deteriorate over time, and the engine may not start up just for this reason. In this case, the old fuel is drained and fresh fuel is poured in its place.

Candle check

Unscrewed the candle

The condition of the candles can be compared with an open book. you just need to be able to read. The table below will help you figure this out.

Candle Status Table

Check for power

The spark must be powerful

It is not difficult to check whether there is actually a spark on the candle. For this, the tip is removed, the candle is twisted, and the tip is again put on it. The candle must be placed on the engine casing, the ignition turned on and the crankshaft cranked intensively. a clearly visible spark should slip from the anode to the side electrode.

A very high voltage is applied to the candle. on the order of several thousand volts. If you hold the candle in your hands during the test, then the electric shock will be very painful. Also, it does not need to be held by hand, pressing it to the engine body, since you can not accidentally hold it, and then again you can check the "by touch" current strength.

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Even if the spark is strong, this is not yet the main indicator of the efficiency of the spark plug, since if compression occurs in the engine, it may become weaker or disappear altogether. It can be checked under pressure in a special device.

Checking the operation of a candle under pressure

In some cases, the cuff may cause the problem. It has a resistor that protects against radio interference, and its burnout causes the spark to disappear. You can check it by removing the high-voltage wire from it, and connecting it directly to the candle. Verification is carried out exactly as described above.

A high voltage wire may also fail. If it has a thick central core, then it can only be pierced, and the spark will go to the body. If a thin wire is wound inside the wire, then the probability of its burnout is very high.

Sometimes it happens that the contacts of a circuit breaker burn up or it simply fails. You can simply bridge the terminals with a screwdriver. If a spark has appeared after these steps, the switch must be replaced.

If there is still no spark, then the malfunction may be in the hall sensor or in the electronic ignition unit. In this case, to check and eliminate the malfunction, take the saw to the workshop.

So, having figured out possible problems and eliminating them, we will proceed to adjust the carburetor.

The cause of unstable engine operation may be poor compression. In this case, adjustments can achieve insignificant results.

Adjust the carburetor

Designation Screw Designations

In fact, adjusting the carburetor is not as difficult as it might seem.

No need to fill in cheaper gasoline. Not only will the engine not develop the required power, you will also have to adjust the carburetor for this fuel. In addition, low-octane fuel consumption will increase.

The bulk of the carburetors are regulated by three screws. The efficiency of work, the power of the chainsaw and fuel consumption depend on how well the tuning is done.

Carburetor Adjustment Bodies

Consider what role each of the screws performs.

  • T. Regulates engine idle. (On some models, it may be labeled S3; LA). With its help, minimum revolutions are set at which the engine will work stably.
  • N. Management of the main jet. He is responsible for the maximum speed. Essentially, this is a fuel metering regulator.
  • L. Quality control of the mixture to stabilize the engine at idle.
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With branded chainsaw models, the manufacturer provides an operating manual, which also contains standards for adjusting the carburetor of an existing unit. In the remaining cases, the screws H and L are fully tightened and then twisted one and a half turns. So the basic settings are made, the final adjustment is carried out only on a warm engine.

Setting the carburetor on a warm engine

Replacing the air filter

The carburetor is only adjusted after cleaning or replacing the filter.

The engine warms up for several minutes and only after that you can begin to set up the carburetor.

  • Release the handle that controls the throttle. the engine must not stall. You can slightly increase the speed (screw T), but only so that the chain does not begin to rotate.
  • We begin to slowly tighten the screw L. We do this until the engine speed starts to fall.
  • It is necessary to check how the engine works at high speeds, and then abruptly dump gas. If the engine worked fine, but then stalled, you can increase the speed by screwing in the screw T.
  • How high are the engine rpm? You won’t check it without a tachometer, but don’t think that the more the better. They can be increased or decreased by screw N. over, to increase the speed, the screw must be screwed in, and to decrease it, unscrew it.

If all the adjustments are made by oneself correctly, the engine will work without interruptions. The following conditions must also be met:

  • At idle, the engine remains stationary.
  • The chainsaw needs to be responsive to the accelerator control, quickly gaining momentum.

Chainsaw in action

If the chain of the chainsaw is dull, then the load on the motor will increase. Sharpening the chain will help correct the situation.

It remains to check the operation of the unit under load. If everything is fine, then you can start to work, if the motor is intermittent, losing power, etc., then you need to try again to make adjustments or consult a specialist.


See how to adjust the idle speed of the STIHL MS chainsaw carburetor:

What to do if the chainsaw does not start because it floods candles? You can get the answer by watching the video: