You start the chainsaw engine with the choke engaged, but now you can’t keep it running unless the choke is on or at half-choke.
A Craftsman chainsaw only runs with the choke on when the engine is getting too much air or not enough fuel.
This may be due to old gas, a punctured or clogged fuel line, a plugged fuel filter, a clogged fuel vent, a bad carburetor gasket, or a dirty carburetor. The chainsaw may also need a carburetor adjustment.
Before performing repairs on your chainsaw, always remove the spark plug boot for safety. Wait for the engine to cool and for all parts to stop moving.
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Follow all safety instructions provided in your equipment operator’s manual before 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.
This is Why a Craftsman Chainsaw Only Runs With the Choke On
Old gas is often the reason why a fuel restriction forms in your Craftsman chainsaw.
A reduced amount of fuel to the engine may require you to use the choke to reduce the amount of air getting to the engine. This is to correct the ratio of gas-to-air required for combustion.
Effects of old gas:
- Ethanol (used in most gas) attracts water to the fuel system.
- Water and ethanol separate from the fuel over time.
- Develops varnish and sticky deposits.
- Clogs the fuel system.
- Degrades fuel components.
When you find the gas in your chainsaw is old, it’s best to drain the tank and refill it with a fresh gas and oil mixture.
Add a fuel stabilizer like Sea Foam or STA-BIL to the fuel to assist with cleaning out the fuel system and reducing moisture.
Once you refill the tank with fresh fuel and a stabilizer mix, start and run the chainsaw for several minutes to work the treated fuel through the chainsaw to loosen the sticky substances.
Reduce the negative effects of fuel by following these tips:
- Use gasoline with a minimum octane rating of 87.
- Don’t use gasoline with an ethanol content greater than 10%.
- Mix the gasoline with a premium 2-cycle oil at a ratio of 50:1 for Craftsman 2-cycle chainsaws.
- Store fuel in a dry location.
- Consume the fuel within 30 days before it begins to break down or add a fuel stabilizer to make it last a little longer.
To learn more about the right fuel to use, check out this article on choosing and storing gas for a Craftsman chainsaw.
Clogged Fuel Filter
A fuel filter’s function is to keep dirt and other contaminants out of the fuel system. You will find the fuel filter for your Craftsman chainsaw inside the fuel tank.
It is a small cylinder-shaped part attached to the fuel line. When the filter isn’t changed regularly, it can become plugged with dirt. This will restrict the amount of fuel that is able to pass through the filter.
When there isn’t enough fuel to mix with air, you may have to run the chainsaw with the choke partly on to correct the ratio of air mixed with gas so the chainsaw continues to run.
Replace your Craftsman fuel filter:
- Wipe around the fuel tank cap before removing it to avoid contaminating the fuel tank.
- Take note of the placement of the fuel filter inside the fuel tank so you install the new one in the same place.
- Pull the filter out of the tank. A clean bent wire or needle nose pliers work well for this.
- Remove the fuel filter from the fuel line and install a new one.
- Place the filter back inside the fuel tank.
- Reinstall the fuel cap.
Punctured or Clogged Fuel Line
The choke may need to be on when the fuel line is clogged preventing a good fuel flow or air is being introduced to the fuel system through a puncture in the fuel line.
When the fuel line is clogged, the clog must be removed. To do this, remove the fuel line from the chainsaw. Spray carburetor cleaner into the line to loosen the clog. Follow by blowing compressed air into the line to remove the clog.
Reinstall the line once the blockage has been removed. If you can’t open up the line or you find the fuel line is dry and cracked, you should replace it with a new one.
Look for a puncture in the line where air can be sucked into the fuel system providing additional air to the cylinder and making the choke necessary to correct the amount of air.
Plugged Fuel Vent
There is a small circular vent on a Craftsman chainsaw. This vent is needed to allow air to pass through it so air is allowed to enter the tank when fuel is used and leave the tank when the fuel tank is filled.
When the fuel tank is unable to vent properly, the tank will form a vacuum restricting fuel from flowing out of the tank. This will reduce the amount of fuel supplied to the carburetor.
Test for a clogged fuel tank vent:
- Use a gauge to test vacuum pressure. If you don’t have a gauge, proceed with the following steps.
- Place the chainsaw on a level surface.
- Start the saw and place the choke in the off position.
- If it begins to run sluggishly, loosen the fuel cap to allow air into the tank.
- If the engine begins to run better after you loosen the cap, it is likely the fuel tank vent is clogged.
Replace a plugged fuel tank vent. On most Craftsman chainsaws, you will find a small cylinder-shaped part called a fuel tank vent installed into the body of the chainsaw just in front of the handle.
Bad Carburetor Gasket
A carburetor gasket, located behind the carburetor, can deteriorate allowing air into the system because the gasket no longer seals correctly. This causes a Craftsman to run lean when there is more air than fuel in the cylinder than the engine requires.
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.
The carburetor’s function is to regulate the amount of fuel that is mixed with air to form combustion to start and run your Craftsman chainsaw.
A buildup of varnish and deposits can clog the fuel passageways and make the carburetor unable to 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
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. You can find these screws on the side of the chainsaw near the pull starter.
The screws are labeled “L” for low-speed “T” for idle speed and “H” for high-speed. Start and let the chainsaw warm up for a few minutes before making adjustments to the carburetor.
Before adjusting the carburetor, make sure the air filter is clean and that the air vents are clean.
Adjusting a Craftsman chainsaw carburetor:
- Start with the L Screw – With the chainsaw idling, turn the screw clockwise until it seems like it’s going to shut off, and then turn the screw slowly counter-clockwise until you achieve a smooth engine idle. Press the throttle and ensure there is a smooth transition as it revs. Make small adjustments until you find the best setting for a smooth operation.
- Adjust the T Screw: This is to adjust the idle speed so the chain doesn’t move while idling. To ensure the T screw is in the correct position, turn the screw clockwise until the chain just begins to move. Then turn the screw slowly the opposite way or counter-clockwise until the chain stops.
- Adjust the H Screw: This screw adjusts the fuel and air mixture at high RPMs. Turn the screw counter-clockwise until it comes to a stop without forcing it. It should begin running sluggish. Slowly turn the screw clockwise until the engine begins to run smoothly. Press the throttle to make sure it accelerates smoothly. Do not over-adjust and try to run at the highest RPMs possible or you could end up damaging the engine.
Many chainsaws have limiter caps to prevent the user from adjusting the carburetor too much. Some chainsaws also require special tools to adjust the carburetor.
If you continue to have problems with the carburetor and are unable to adjust it or unsure how to adjust it, contact your local Craftsman service center for help.