Even though you are still able to run your trimmer using the choke to restrict air, you need to find out why you have to do this to correct the problem and avoid additional damage.
A Husqvarna string trimmer only runs with the choke on when the engine is getting too much air or too little fuel.
This may be the result of a fuel restriction due to a dirty carburetor, plugged fuel filter, clogged fuel line, plugged fuel tank vent, or old fuel; or the result of excessive air due to a punctured fuel line or a bad carburetor gasket.
Remove the spark plug wire prior to making any repairs. Be cautious and follow all safety procedures in the Husqvarna operator’s manual.
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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.
Husqvarna String Trimmer Only Runs With the Choke On or Half On
1. Old Gas
It’s best to only purchase gas that can be consumed within 30 days. This is because gas can begin to break down potentially causing the engine to run sluggish because it’s not getting enough fuel.
You may find the only way you’re able to keep the mower running is by using the choke to correct the fuel-to-air ratio needed for combustion.
Gas that contains ethanol attracts moisture to the fuel system. When it breaks down, the ethanol and water mixture separates from the gas. It leaves behind varnish that can restrict fuel flow or cause component failure.
Ethanol is not good for a small engine. Never use fuels with high ethanol content. Avoid fuels sold as E15 and E85 as they contain up to 15% and 30% respectively.
A Husqvarna string trimmer requires an unleaded gas that has a minimum 89-octane rating that contains no more than 10% ethanol.
- Husqvarna 2-cycle string trimmers: Require a gas and 2-cycle oil mixture at a ratio of 50:1.
- Husqvarna 4-cycle string trimmers: Require gas only (no oil is mixed).
Read more about choosing and caring for the gas at This is the Gas and Oil Husqvarna String Trimmers Use (2 & 4 cycle).
Add the fuel mixture to the fuel tank. Start your Husqvarna trimmer and allow it to run for about 5 minutes to run the treated fuel through the system.
If the trimmer doesn’t begin to run well without the choke on, continue checking the items below.
2. Clog or Puncture in the Fuel Line
A clog in the fuel line will narrow the opening in the line causing the engine to receive a reduced amount of fuel.
A puncture in the fuel line may cause additional air to be sucked into the fuel system providing too much air to the engine.
Both a clog and a puncture may cause your Husqvarna to only run with the choke on.
SOLUTION: Remove and replace a clogged or punctured fuel line.
3. Plugged Fuel Filter
Another item that can restrict fuel flow is a plugged Husqvarna fuel filter. A fuel filter is used to prevent dirt and other debris from running through the fuel system and engine.
When the filter isn’t changed regularly or you’re running very dirty fuel, it can become plugged not allowing sufficient fuel to pass through the filter. It’s best to stay on top of your fuel filter maintenance by changing it out annually.
SOLUTION: Replace a plugged fuel filter. The filter is located inside the fuel tank. Wipe around the fuel tank cap before removing it to keep dirt from falling into the tank. Pull the filter out of the tank.
A clean bent wire works well to hook the fuel linen to pull the filter out of the tank. Remove the old filter and attach a new fuel filter to the end of the fuel line and place it back inside the fuel tank. Reinstall the fuel cap.
4. Bad Carburetor Gasket
The gasket that sits behind the carburetor can deteriorate and become worse over time. When this happens, it no longer seals properly allowing additional air into the system causing it to run lean.
This is when there is a higher concentration of air and less fuel than required by the engine.
SOLUTION: Gain access to the carburetor and carefully remove the linkages and bolts attaching the carburetor. Remove the carburetor and gasket.
Reinstall a new gasket and reattach the carburetor, bolt, and linkages. You may need to clean the carburetor while it is removed from the Husqvarna trimmer.
5. Dirty Carburetor
The carburetor’s function is to regulate the amount of fuel that is mixed with air to form combustion to start and run the string trimmer.
A buildup of varnish and deposits can make the carburetor not function right so it isn’t able to get fuel to the engine.
SOLUTION: If you are a little mechanical you should be able to handle cleaning your carburetor. Clean the carburetor by taking it apart and using a carburetor cleaner to remove deposits left behind from old fuel.
If the carburetor does not function after being cleaned, you may need to be able to find a rebuild kit to rebuild the carburetor or you may have to replace it.
Carburetors for a Husqvarna string trimmer can run between $30-$70 depending on the model of your string trimmer.
6. Plugged Fuel Tank Vent
The fuel tank must have a vent so air can pass into the tank to equalize the tank pressure and air pressure. Without a vent, the fuel tank will create a vacuum that will restrict the amount of fuel getting to the engine.
This may cause you to have to run the trimmer with the choke on. A good indication you may have a fuel tank vent problem is when your Husqvarna trimmer runs for a while before it starts to run sluggish or shuts down.
SOLUTION: Place the string trimmer on a level surface. Loosen the cap and don’t allow gas to spill. Start the trimmer. Place the choke in the off position.
If the trimmer runs well with the choke in the off position, tighten the cap and allow it to continue to run with the choke off. If it dies, you may have to replace the plugged fuel tank vent.
Depending on the model Husqvarna string trimmer you own, you will find the fuel tank vents out of a part attached to the end of a line coming out of the fuel tank or built into the fuel cap.