How Does a Chainsaw Carburetor Work?

How Does a Chainsaw Carburetor Work?

The carburetor, a critical engine component, influenced the performance of tiny engines. A poorly maintained carburetor causes many engine issues. In order to better understand how a chainsaw carburetor functions and how to keep it in good working order, this post will go into greater detail.

How Does a Chainsaw Carburetor Work?

how does chainsaw carburetor work

In chainsaws, the carburetor is made up of a venturi duct that creates a suction to aid pull fuel from jets. A throttle valve controls the delivery of the air/fuel combination to the engine. Fuel flow in the jets of a carburetor can be adjusted using screws that are included with the device. It is possible to manage the engine RPMs by manipulating these screws. A carburetor should be properly maintained besides being adjusted by examining, replacing any worn-out parts, and cleaning the jets regularly.

How is Fuel Drawn into a Chainsaw?

The gasoline and air mixture are combined in the carburetor, which then sends it to the engine through a venturi duct. The airflow in the venturi creates a vacuum that draws the fuel out of the jet.

A carburetor is essentially an air tube with a few fuel-supplying jets inside of it. A venturi is the name of this tube. The air filter sends air into the venturi. The venturi has a small area where the airflow is accelerated, which lowers the air pressure. This reduced pressure causes a spray of fuel to be drawn off of the main jet. This fuel is transported to the engine after mixing with the air in the venturi upstream.

Let’s examine some of the vital parts of a carburetor that support its operation:

Component 1: Throttle Plate

The throttle plate is a butterfly valve that is situated in the venturi. A closed throttle plate causes the engine to idle. In this condition, no fuel is extracted from the main jet and just a little amount of air flows along the venturi. Only the idle jets deliver the gasoline required to maintain the engine at idle. More air may flow down the venturi as the throttle is depressed because the valve opens.

Component 2: Jets and Screws

Idle jets and the primary fuel jet make up most of the fuel jets. At all times, the idle jets are opened; normally, there are three of them. When the throttle plate is kept open, the venturi’s pressure falls to a level where the main jet can supply fuel. These jets have screws at their starting locations that regulate the flow of fuel through them.

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The H screw is used on the main jet, whereas the L screw is used on the idle jets. A screw known as an idle screw (I) is also present on the throttle plate. When the engine is idle, this screw regulates the throttle plate position.

Component 3: Choke Plate:

There is a choke plate, which normally helps when starting a cold engine. At the venturi’s entrance is the choke plate, which resembles a throttle plate. The plate closes the venturi when the choke lever is pulled. As a result, the mixture gets richer as the throttle plate is opened because more fuel is pulled from the main jet while less air is accessible.

Rich fuel mixtures enhance the temperature of an engine, making it easier to start when the engine is cold. The choke plate doesn’t need to be engaged as the engine has already started. As a result, removing the choke lever allows a carburetor to resume normal operation.

How Is The Chainsaw’s Carburetor Adjusted?

You must set the low-speed (L) and high-speed (H) screws on the chainsaw’s carburetor to the proper RPMs and performance levels.

A chainsaw carburetor is made up of three screws: an idle screw (I), a high-speed screw (H), and a low-speed screw (L). These screws each regulate the amount of gasoline the engine receives at low, idle, and high speeds. When it is difficult to keep the engine running or when it overrevs, think about adjusting these screws to optimize the engine RPMs.

Understanding Screw Adjustment 

The purpose of screw adjustment is to regulate the amount of fuel that gets to the engine. When a screw is loosened, more fuel can mix with air, which results in a richer mixture. Rich mixture engines operate at comparably lower RPMs. By restricting fuel flow, tightening the screw causes the mixture to become lean, which increases engine revs. As a result, when the screw is tightened, the RPMs rise, and as it is loosened, they decrease.

Make sure you are aware of this before you change your carburetor. We’ll walk you through adjusting a chainsaw’s carburetor step by step below:

Step 1

Make sure the air filter is clean and the spark arrestor is free of carbon buildup before tuning the carburetor. Always let your saw idle for a few minutes and keep the tank halfway full to get the greatest tuning results.

  • Air filter: Always check and thoroughly clean the air filter before adjusting or tuning the carburetor. The air-fuel mix is disturbed when the air filter is cleaned after the carburetor has been set, which makes the saw run lean.
  • Exhaust muffler: You should also check for carbon buildup and clean the spark arrestor screen in your exhaust muffler.
  • Petrol level: During tuning, make sure the tank is always half-full with petrol. If the carburetor is set on an empty tank, the engine may run lean.
  • Idle: Never tune a carburetor with a cold engine. When the engine reaches operating temperature, doing this would cause the carb setting being rich. It is advisable to wait a few minutes for your saw to idle before making the adjustment.
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Step 2: Adjust the L and H Screws on a Carburetor

Use a flat head screwdriver to turn the screws while paying close attention to how the RPM varies with each turn.

Screw 1: Change of Low-Speed Screws:

To perform the low-speed screw adjustment, according to the steps listed below:

Step 1: Start the engine.

Pull the chord to start the chainsaw. Give the machine a few seconds to run idle. Observe whether the engine idles without dying or runs smoothly.

Step 2: Raise the L screw.

If the engine shuts off when the engine is idling, increase the idle RPM by tightening the Low Speed (L) screw using a screwdriver. The RPMs will drop as you tighten it even more. Note where that point is in your mind. From then, loosen the screw, allowing the RPMs to increase once again until they decrease. Note the second point from which the RPMs decline.

Step 3.: Locate the right location

Now, anyplace between these two places should be the optimal screw setting. Once the ideal balance has been achieved, leave the screw in place. The engine may be kept running at its idle RPMs. The engine will react considerably more quickly and without lag when you press the trigger.

Screw 2: Idle modification

The mixture may be sufficiently lean after the L change to engage the clutch, and the chain may move. If your chain spins, remove the idler screw until it stops. This is essential since an idle spinning chain can be seriously damaging. Go straight to the following step if your chain doesn’t rotate.

Screw 3: High-Speed Adjustment: 

The high-speed screw controls the engine’s maximum RPMs. The chainsaw may overrev when the throttle is depressed if the screw is too tight. Because it can damage the piston besides scoring the cylinder walls, an over-revving chainsaw can seriously harm your engine and raise the possibility of a complete engine seizure.

A digital tachometer is useful to have nearby when adjusting your high-speed screw so you can record the RPMs. The ideal H screw setting can be found in your device’s manual, if one is not accessible.

Step 1: Start-Up

Pull the trigger to increase the RPMs on your chainsaw after starting it.

Step 2: Narrow the screw.

With the throttle fully open, tighten the H screw. The saw will then operate at its highest RPMs. The tachometer reading now indicates the maximum engine RPMs; note this.

Step 3: Set the screw accordingly.

In order to decrease the maximum RPMs at WOT by 1000–2000, loosen the screw by half a turn. That is the setting that is best for your engine. Keep your engine running at a few thousand RPMs below the maximum RPMs recommended.

After finishing this step, your chainsaw will be correctly calibrated to run at an ideal speed without lag.

How to Fix a Chainsaw Carburetor?

Chainsaw carburetors frequently clog, potentially because of leftover fuel. Thus, maintaining chainsaws must include cleaning these jets.

Carburetors need to be kept clean and free of buildup of debris besides being properly set. Nowadays, ethanol is frequently incorporated with the fuel. As a result, when maintained for an extended period, it often develops sticky white deposits. These buildups may cause the carburetor’s jets to become clogged and reduce performance.

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How To Tune A Carburetor?

  • To warm up your saw, turn it on and let it run for a while. Your saw should be put down, given a 30-second break, picked up, leaned forward, the handle raised, and the bar lowered.
  • To lessen the amount of gasoline entering the carburetor if the automobile starts to stall, tighten the low-speed screw. Whenever the idle saw “dogs,” let go of the low-speed screw.
  • As a result, more gasoline is introduced into the carburetor. So it’s good if the idle saw “flutters” when being revved, but bad if it “screams” when being revved. As a result, keep listening!
  • Simply loosen the high-speed screw if the chain won’t move, and you’re done. Do not panic; this problem may be resolved in a matter of seconds and, if ignored, might be very harmful. If the chain spins while the engine is running, adjust the idler screw as necessary to stop it.
  • In the absence of a tachometer, which helps prevent engine overheating, your owner’s handbook can advise against carburetor adjustment.
  • If you have a tachometer, that’s excellent. If not, you can still tune the carburetor using the techniques listed above, just be careful not to overrev the engine.

Final Word

In conclusion, the chainsaw carburetor is essential to the chainsaw’s operation. To ensure effective combustion and engine performance, it is to mix fuel and air in the right proportion. The carburetor uses a variety of components to control the flow of fuel and air into the engine, including the throttle valve, fuel jets, and mixture adjustment screws. Knowing how the chainsaw carburetor works and how to repair it can help you ensure your chainsaw operates smoothly, efficiently, with maximum power, and with the least amount of gasoline consumption. For carburetor upkeep, including cleaning, adjusting, and replacing any broken parts, according to the manufacturer’s directions.


What governs a carburetor’s operation?

Based on the Bernoulli principle, the carburetor draws more gasoline into the airstream as engine speed increases because the static pressure of the intake air decreases. Mostly, when a driver presses the throttle pedal, less fuel enters the engine (except for the accelerator pump).

Which two types of carburetors are there?

There are a variety of sizes and layouts available for carburetors. Carburetors come in two varieties: Fixed venturi – The fuel flow is controlled by the airflow’s velocity. Variable venturi: The airflow is regulated with the fuel flow, which is mechanically controlled.

How is fuel pushed into the carburetor?

The engine would sputter because of this. Most carburetors use an accelerator pump, which is simply a gasoline squirt gun that squirts fuel into the carburetor’s throat to enrich the air-fuel combination in the fleeting period before engine vacuum returns, to remedy this issue.

What function does a carburetor serve?

A carburetor is a tool that help blend fuel and air in order to allow internal combustion inside an internal combustion engine. An internal combustion engine’s intake manifold receives the fuel and air mixture from this mechanism, which delivers the mixture to the cylinders.

Why is a carburetor necessary?

The carburetor’s role is to control the ratio of gasoline to air so that the proper combustible combination is produced. Your carburetor’s other function is to regulate engine speed. By regulating how much of this air and fuel mixture is permitted to enter your engine, your throttle regulates the speed.

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