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Your Chainsaw Loses Power (Find Out Why!)

You have a big job ahead of you, but your chainsaw isn’t up to the task. It is running sluggishly and losing power.

A chainsaw loses power when it no longer gets the amount of air, fuel, and spark required to form combustion in the engine. This may be due to a dirty carburetor, plugged fuel vent, plugged air filter, clogged spark arrestor, dirty spark plug, or carburetor out of adjustment.

Keep reading for additional items that can result in a loss of power. Follow all safety precautions outlined in the chainsaw operator’s manual including removing the spark plug wire, waiting for all parts to stop moving, and letting the engine cool before you begin repairs.

Things that cause your chainsaw to lose power:

  • Plugged air filter
  • Clogged spark arrestor
  • Clogged fuel filter
  • Plugged or punctured fuel line
  • Old fuel
  • Dirty carburetor
  • Plugged fuel vent
  • Dirty spark plug
  • Carburetor requires adjustment
  • Chain brake is engaged
Chainsaw loses power

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Follow all safety instructions provided in your equipment operator’s manual prior to diagnosing, repairing, or operating. Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.

Lack of Air Causes a Chainsaw to Lose Power

Air is required for a chainsaw to run well. When the chainsaw doesn’t get sufficient air, the saw can begin to bog down and lose power. Check for items that will restrict airflow including a plugged air filter and clogged spark arrestor.

In addition to checking these items, ensure the choke is in the correct position. The choke is used to start a cold engine and must be adjusted to the off/run position once the engine warms or it will begin to lose power and die.

Plugged Air Filter in a Chainsaw

An air filter is used on the saw so the engine doesn’t pull in dirt and sawdust from the dirty conditions created by running the saw. When dirt enters the carburetor throat it can cause wear and permanent engine damage.

The air filter must be cleaned or replaced regularly. When it isn’t, the filter can develop a buildup of dirt and debris that will restrict the amount of air that is able to pass through the filter. A plugged air filter will cause a loss of power.

When your air filter becomes so plugged it restricts airflow, you should replace it with a new one. Never run your chainsaw without an air filter. Doing this can result in significant engine damage.

Clogged Spark Arrestor on a Chainsaw

A spark arrestor is located on the muffler of a chainsaw. It is a small screen that prevents hot exhaust material from shooting out of the chainsaw and causing injury or a potential fire.

This screen can become plugged with carbon buildup. You may experience a loss of power where the chainsaw won’t run at full RPMs. This is because the engine isn’t able to exhaust properly.

This screen should be checked often and cleaned to prevent buildup. To do this, first, disconnect the spark plug wire and wait for the saw to cool down.

Carefully remove the spark arrestor screen. Clean it using a small metal brush. If you find any damage or holes in the screen, replace it with a new spark arrestor screen.

Once you have installed a new or clean spark arrestor, reattach the spark plug wire if you are done performing all repairs and maintenance.

Lack of Fuel Causes a Chainsaw to Lose Power

Fuel is another main item that can cause your chainsaw to not give you a lot of power. If the engine isn’t getting enough fuel, it will bog down and run sluggishly. Look at the fuel system and all items that can restrict fuel supply.

Old Fuel in a Chainsaw

If you find the fuel in your chainsaw is old, begin by draining the fuel tank and adding fresh fuel. Read more about the right fuel for your chainsaw here.

Adding a fuel additive like Sea Foam to the fuel will help clean out the fuel system. Then continue with checking for a clogged fuel filter; plugged or punctured fuel line; or dirty carburetor.

Clogged Fuel Filter on a Chainsaw

The fuel filter can be found inside the fuel tank. It is attached to the end of the fuel line to strain the fuel in the tank. Its purpose is to keep dirt and debris from entering the fuel system.

When the fuel filter is not changed out regularly or you are using very dirty fuel, it can become plugged keeping a sufficient amount of fuel from flowing through the filter. This lack of fuel flow will cause a chainsaw to lose power.

You will find the fuel filter on a chainsaw located inside the fuel tank. It’s a small cylinder-shaped part attached to the end of the fuel line.

In order to access the filter, wipe around the fuel tank cap to remove loose dirt, remove the cap, and use a clean bent wire to hook the fuel line and pull the fuel filter out of the tank.

Plugged or Punctured Fuel Line on a Chainsaw

Old fuel sitting in the chainsaw is likely to leave behind varnish and sticky deposits that clog the fuel line. This can restrict fuel flow.

When you find there is a clog, remove the fuel line and clean it to remove the clog using carburetor cleaner. Spray the carburetor cleaner into the line to loosen the clog. Then blow compressed air through it to remove the clog.

Repeat spraying the cleaner and blowing compressed air until the line is free of the blockage. Replace with a new line when you find it is dry or cracked.

Another thing to look for is a punctured fuel line. A punctured line can introduce air into the fuel system. Additional air to the cylinder can make your chainsaw lose power when there is no longer a correct mixture of fuel and air.

Dirty Carburetor on a Chainsaw

The carburetor mixes the correct proportion of air and fuel required for a chainsaw to start and continue to run. The passageways can become clogged and the small components can fail to function correctly which can be the reason the chainsaw starts running sluggishly.

Old fuel is a big reason why a carburetor will stop working. You may be able to clean or rebuild your carburetor to get it working again. You will have to replace the carburetor if this doesn’t work.

Carburetor Needs Adjustment on a Chainsaw

The carburetor may need to be adjusted to change the RPMs at idle speed and at full throttle. It may be causing the engine to run lean resulting in the need for the choke to be on.

There are adjustment screws on the carburetor to make these adjustments. On most chainsaws, you will find three adjustment screws: low speed, high speed, and idle speed.

Let the chainsaw idle and adjust the low-speed screw clockwise and counter-clockwise until you find the “sweet spot” where it runs smoothly and not sluggishly.

Next, adjust the high-speed screw to get a good smooth RPM at full throttle. Don’t over-adjust and allow the RPMs to increase too much or you will damage the engine. You may need to adjust the idle screw if your chain moves at idle.

Some chainsaw manufacturers have limits to the adjustments that the owner can perform to the carburetor. If you are continuing to have problems with the carburetor or your model Husqvarna doesn’t allow you to make the carburetor adjustments, bring your chainsaw to your local chainsaw dealer.

A special tool may be required so only your dealer can make the necessary adjustments.

Plugged Fuel Vent on a Chainsaw

The fuel tank must vent to equalize the internal tank air pressure to the atmospheric air pressure. When the vent becomes plugged and air can no longer pass through the vent, the fuel tank will form a vacuum and starve the engine of fuel.

The fuel tank vent on your chainsaw may be an independent small cylinder installed on the chainsaw to allow the tank to vent. On some chainsaws, you will find the fuel tank vent built into the fuel cap assembly.

Test whether you have a clogged fuel tank vent using a vacuum tester. Don’t worry if you don’t have a vacuum tester, you can use this method:

  • Place the saw on a level surface.
  • Start it.
  • Remove the choke. Loosen the cap to allow air to enter the tank to see if the engine runs better.

If it does, tighten the fuel cap and run the saw to see if it begins to run sluggish again until you loosen the cap to allow air into the tank. You will need to replace the fuel tank vent if you find the issue can be replicated.

Lack of Spark Causes a Chainsaw to Lose Power

Spark is required to ignite the fuel and air mixture to form a combustion in the cylinder so the chainsaw will continue to run. When the chainsaw isn’t getting consistent spark, it will bog down and lose power.

Dirty Spark Plug in a Chainsaw

The spark plug is a wear item. It must be replaced regularly. I recommend replacing it once a year for casual usage. However, if you are using your chainsaw often, you will need to change it more frequently.

The spark plug will become dirty over time causing an intermittent spark and a loss of power. Remove the spark plug and inspect the tip. If it is dirty, but not very dark in color, you can try to clean it using a wire brush so you can reuse it.

If you find the spark plug is very dark in color, and has a broken porcelain, or a burnt electrode, you must replace it with a new one.

Other Item That Causes a Chainsaw to Lose Power

Chain Brake is Engage on a Chainsaw

The chain brake is a plastic handle that sits in front of the regular handle you use to hold the chainsaw. This is a safety feature installed to protect the user when the saw kicks back.

When the chain brake is engaged, the chainsaw will bog down losing power. Check the chain brake and make sure it is in the off position.