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7 Reasons a Chainsaw Only Runs With the Choke On (FIX IT!)

It’s frustrating when you have to engage the choke lever to half choke or more to keep the chainsaw running. This is not normal and the problem must be found and fixed to keep the chainsaw performing at its best.

A chainsaw only runs with the choke on when the engine is getting too much air or not enough fuel. This may be due to a plugged fuel filter or fuel tank vent; a punctured or clogged fuel line; a dirty carburetor; a bad carburetor gasket; or the carburetor needing adjustment.

Prior to completing repairs, follow the safety procedures outlined in your operators manual. This includes removing the spark plug wire.

Chainsaw only runs with the choke on

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

Reasons a Chainsaw Only Runs With the Choke On

Old Fuel in a Chainsaw

Running old fuel through a chainsaw can have negative effects on the fuel system. This is because most fuels today include ethanol, an alternative fuel, that attracts moisture to the fuel.

The water and ethanol mixture can damage the carburetor and also leave behind gummy deposits that restricts fuel supply. To minimize problems caused by old fuel, choose a fuel that has a maximum ethanol content of 10%.

Because ethanol isn’t good for the small engine on a chainsaw, the lower the ethanol content the better. Purchase and consume fuel within 30 days for best performance. Add a fuel stabilizer to make it last a little longer if there is a chance you are not going to be able to consume it within this time.

Most chainsaws utilize 2-cycle engines which requires a gasoline and oil mixture. Some 2-cycle engine oils contain a fuel stabilizer. They may keep your fuel stable anywhere between 30 days and 2 years depending on the manufacturer of the oil.

Another option to add to the gas and oil mixture for a 2-cycle chainsaw or gasoline for a 4-cycle chainsaw is Sea Foam Motor Treatment or STA-BIL. Both of these options stabilize fuel and reduce moisture.

When you find you have gas that’s been sitting in your saw for a long period of time, its best to drain the tank and refill with a fresh fuel and stabilizer. Once you refill the tank with a fresh fuel and a stabilizer, start and run your chainsaw for several minutes to work the treated fuel through the chainsaw.

Fuel for a 2-Cycle Chainsaw Engine

  • Requires a gas and oil mixture at a ratio of 50:1 or 40:1 depending on the manufacturer. Check out the chart in this guide for a list of manufacturers and their fuel requirements.
  • Use a gasoline with a minimum octane rating of 89.
  • Don’t use gasoline with an ethanol content greater than 10%.
  • Mix in a 2-cycle premium oil. This oil is not the same as standard engine oil.
  • Consume fuel within 30 days
  • Add a fuel stabilizer to fresh gasoline so it lasts a little longer when you are unable to consume fuel quickly
  • Store fuel in a dry location.

Fuel for a 4-Cycle Chainsaw Engine

  • Requires a gasoline with a minimum octane rating of 89 and a maximum 10% ethanol content. Do not mix with oil.
  • Consume fuel within 30 days.
  • Add a fuel stabilizer to fresh gasoline so it lasts a little longer when you unable to consume fuel quickly.
  • Store fuel in a dry location

Plugged Fuel Filter in a Chainsaw

The fuel filter is designed to strain fuel before it gets fed through the fuel line and into the carburetor. This is to keep dirt and debris out of the fuel system and engine.

When the filter isn’t changed out regularly, it can become plugged causing less fuel than usual to pass through the filter. Without sufficient fuel, you may have to run with the choke partially on or at half choke to restrict the amount of air because you are no longer getting a good supply of fuel.

The fuel filter is a cylinder shaped component attached to the fuel line located inside the fuel tank. Change out the fuel filter with a new one by first wiping around the fuel tank cap to keep dirt from falling inside the tank.

Next, pull the fuel filter out of the tank using a clean bent wire. Securely hold the fuel line while pulling the filter out of the line. Insert a new fuel filter and place it back inside the fuel tank. Reinstall the fuel tank cap.

Punctured or Clogged Fuel Line on a Chainsaw

Again, the choke may need to be on when the fuel line is clogged preventing a good flow of fuel. It may also be due to air being introduced to the fuel system through a puncture in the fuel line.

Inspect the fuel lines. Look for a clog that can cause a fuel restriction or a puncture that may allow air into the fuel system.

If you find either problem, you should replace the fuel line. You can attempt to clean and remove the clog in the fuel line before replacing it. Remove the line from the chainsaw, spray carburetor cleaner into the line to loosen the clog and blow compressed air through the line to remove the clog.

Plugged Fuel Vent on a Chainsaw

There is a small circular vent on a chainsaw that allows air to pass through the tank so the atmospheric pressure stays equal to the fuel tank pressure. Some chainsaws won’t have this circular vent on the tank and you may find the tank vents through the fuel cap.

When the fuel tank is unable to vent properly, the tank will build pressure forming a vacuum that will restrict fuel flowing out of the tank. This will reduce the amount of fuel supplied to the carburetor.

To test whether you have a clogged fuel tank vent, use a vacuum tester. If you don’t have a vacuum tester, you can place your saw on a level surface, start it, and remove the choke. If it begins to run sluggish, loosen the fuel cap to allow air into the tank.

When the chainsaw starts and runs fine after allowing air into the tank, you may have a problem with the fuel tank vent. You can continue to run the saw to see if you can replicate the issue where is runs sluggish or shuts down until you loosen the cap to confirm the problem.

If you find loosening the cap solves the problem where you no longer need to run the saw with the choke on, replace the vent.

Bad Carburetor Gasket on a Chainsaw

The carburetor gasket, located behind the carburetor, can deteriorate allowing air into the system when the gasket no longer seals correctly. This will cause your chainsaw to run lean when there is more air than fuel in the cylinder than it requires to run.

Access the carburetor and carefully remove the linkages and bolts attached to the carburetor. Remove the carburetor and gasket. Install a new carburetor gasket.

Before you install the carburetor, check it out. You may need to clean it while you have it off the chainsaw.

Dirty Carburetor on a Chainsaw

The carburetor’s function is to regulate the amount of fuel that is mixed with air to form a combustion to start and run your chainsaw. A buildup of varnish and deposits can make the carburetor not correctly perform this function.

If you are a little mechanical you should be able to handle cleaning your carburetor. Clean the carburetor by taking it apart and using carburetor cleaner to remove deposits left behind from old fuel.

If the carburetor does not function after being cleaned, you may need to rebuild it or replace it with a new carburetor.

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 to until you find the “sweet spot” where it runs smooth and not sluggish.

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.