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12 Reasons a DeWalt String Trimmer Won’t Start (SOLVED)

A DeWalt string trimmer won’t start when due to a dirty carburetor, plugged air filter, bad spark plug, bad starter solenoid, clogged fuel line, plugged fuel filter, wrong fuel mixture, broken recoil starter, plugged spark arrestor, or old fuel.

Keep reading for additional items that may cause your starting problem.

Always remove the spark plug boot and wait for all parts to stop moving before starting any repairs.

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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.

Reasons For Your DeWalt String Trimmer Starting Problem

1. Old Fuel in a DeWalt String Trimmer

Not consuming the fuel right away and allowing it to sit in your DeWalt string trimmer is often the unlying cause for fuel restrictions and component failures.

Gasoline can begin to break down as soon as 30 days after purchase. Most gasoline sold today includes ethanol. This is an alternative fuel that attracts moisture to the gas.

Water does not mix with gas. Instead, the ethanol and water mixture will separate from gas. It will leave behind varnish and is corrosive.

It’s important to choose a fuel that has a low ethanol content and consume it within 30 days.

Solution: Drain any old fuel remaining in your string trimmer and fill it with fresh fuel. This is an oil and gas mixture for a 2-cycle engine.

Add a fuel stabilizer like Sea Foam Motor Treatment or STA-BIL to clean the fuel system and reduce moisture.

2. Incorrect 2-Cycle Oil Mix in a DeWalt String Trimmer

DeWalt string trimmers require a gas and oil fuel mixture to efficiently lubricate the engine. Using straight gas in a 2-cycle DeWalt string trimmer will damage the engine and cause it to seize.

A 2-cycle DeWalt string trimmer uses gas and oil mixed at a ratio of 50:1. For example, a 50:1 mix equals 50 parts gasoline to 1 part oil.

When creating the oil and gas mixture for your DeWalt string trimmer, use unleaded gasoline with a minimum octane rating of 89 (mid-grade) and no more than 10% ethanol content. Add a 2-cycle premium oil that is ISO-L-EGD and JASO M345 FD certified.

Mix it in an approved gas can before adding it to your string trimmer. Use a 2-cycle engine oil like this oil by Kawasaki. This is a 2.6 oz bottle to mix with 1 gallon of gas for a 50:1 mix.

DeWalt 2-Cycle Gas to Oil Mix

Mixture1 Gallon Gas2 Gallon Gas2.5 Gallon Gas
50:12.6 oz Oil5.2 oz Oil6.4 oz Oil
32:14.0 oz Oil8.0 oz Oil10.0 oz Oil
DeWalt 2-Cycle String Trimmer Gas-to-Oil Mix

Solution: Drain the fuel tank and fill it with the correct gas-to-oil mix. If you continue to have problems, have a small engine mechanic diagnose the problem and determine whether a cost-effective repair can be made.

You can find more information about the right gas to use in your DeWalt string trimmer here.

2-Cycle Premixed Fuel

A great option to reduce fuel problems and extend engine life is using an ethanol-free fuel mix. This is an ethanol-free blend of oil and fuel that is ready to pour into your string trimmer’s fuel tank.

You won’t have to deal with the bad effects of ethanol as discussed in the fuel section. Also, it’s convenient to have fuel available on your shelf when you need it. TruFuel also makes a good 50:1 premixed fuel.

3. Plugged Air Filter in a DeWalt String Trimmer

An air filter is used on your DeWalt string trimmer to protect the engine from dirt and other contaminants that can damage it. The air filter should be changed out annually and cleaned regularly.

When the filter becomes dirty and plugged, sufficient air isn’t able to pass through it. The engine doesn’t get the air it needs to start and run.

Never operate your string trimmer without an air filter, even if it is just for a short period so you can finish a task. Dirt in the engine can cause wearing and significant engine damage which may result in having to buy a new string trimmer.

Solution: Remove the filter and wipe out any remaining dirt from the air filter housing. Replace a dirty air filter with a new air filter.

4. Bad Spark Plug in a DeWalt String Trimmer 

The spark plug is another maintenance item that should be checked. Without spark, your engine will not be able to ignite fuel and air to start the engine.

This is a part that should be replaced annually to keep in good condition. The spark plug can become excessively dirty, the porcelain can crack or the electrodes can become pitted causing the spark plug to fail.

Solution: You can attempt to clean a dirty spark plug with a wire brush and reuse it if it is a little dirty and has no damage or wear. Otherwise, you should replace it.

I prefer to replace it when the mower begins to act up just to make sure it’s not part of my problem. It is an inexpensive part and one of the primary items responsible keep your string trimmer running well.

Make sure your spark plug is gapped to the manufacturer’s specification and the spark plug wire (boot) is securely attached. These items can also affect starting.

ModelSpark PlugSpark Plug Gap
DXGST227CSChampion RDJ7J (USA)
Champion QDJ7J (Canada)
.025 in (.635 mm)
DXGST227SSChampion RDJ7J (USA)
Champion QDJ7J (Canada)
.025 in (.635 mm)
DeWalt String Trimmer Spark Plug and Electrode Gap

5. Plugged Fuel Filter in a DeWalt String Trimmer

The fuel filter can be found inside the fuel tank. It attaches to the fuel line to strain the fuel before it enters the fuel system.

Its function is to keep dirt and debris from getting into the fuel system that may clog the lines and carburetor damage your DeWalt trimmer.

When the fuel filter becomes plugged because it isn’t changed out regularly or you are running very dirty fuel, the amount of fuel allowed to pass through the filter is reduced. This can cause your string trimmer to fail to start because the engine isn’t getting the fuel it requires.

Solution: Locate the fuel filter inside the fuel tank and replace it.

  • Wipe around the fuel cap to remove any loose dirt so it doesn’t fall into the fuel tank once you remove the cap.
  • Gain access to the filter. A clean bent wire works well to “fish” the filter and pull it out of the tank.
  • Remove the old filter from the fuel line. Be careful not to lose the retaining ring securing the line to the filter.
  • Install the new fuel filter securing the fuel line to the filter using the retaining ring.
  • Place the filter back inside the fuel tank and install the fuel cap.

6. Bad Primer Bulb in a DeWalt String Trimmer

A cracked DeWalt primer bulb that won’t fill up with fuel won’t function correctly to get fuel to the carburetor for starting the string trimmer.

Solution: Replace with a new primer bulb.

7. Fuel Line Blocked in a DeWalt String Trimmer

Old fuel sitting in your string trimmer can leave a gummy sticky deposit behind that restricts fuel flow. This can clog the fuel line and restrict the fuel flow your string trimmer requires to start.

Solution: Replace a fuel line on your DeWalt string trimmer when it is cracked, kinked, or clogged.

8. Plugged Fuel Tank Vent in a DeWalt String Trimmer

The fuel tank vent allows air into the tank. Without a vent, the fuel tank will create a vacuum that won’t allow fuel to flow through the string trimmer.

A good indication you may have a fuel tank vent problem is when your string trimmer runs for a few minutes and then shuts down and won’t start until you remove or loosen the fuel cap to allow air into the fuel tank.

When you tighten the cap and allow it to run and the string trimmer dies and fails to start until the cap is loosened, you most likely have a fuel vent problem.

Solution: Replace the fuel tank vent so the air can flow into the fuel tank. Most likely, the fuel tank vent is located in the cap on a DeWalt string trimmer. The cap will need to be replaced.

9. Dirty Carburetor on a DeWalt String Trimmer

The carburetor regulates the amount of fuel that is mixed with air for combustion in the cylinder. Old fuel will gum up and clog the carburetor so it no longer functions properly.

This is a common problem. So common, that many manufacturer’s won’t warranty a carburetor after 90 days.

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 carburetor cleaner to clean it.

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

10. Bad Recoil Starter on a DeWalt String Trimmer

Your DeWalt string trimmer uses a recoil to start the engine. A bad pulley, loose or missing spring, or broken clips can keep your recoil from working.

Solution: You can attempt to replace the spring and restring the recoil. If it does not work because other components in your recoil are damaged, such as the clips or the pulley, you are better off just replacing the recoil assembly.

11. Bad Spark Arrestor in a DeWalt String Trimmer

You will find a spark arrestor in your DeWalt string trimmer that can prevent it from starting. The spark arrestor is a small screen that can get plugged with soot.

Solution: Disconnect the spark plug boot. Make sure your engine is not hot. Remove the engine cover and engine exhaust cover.

Remove the spark arrestor and clean it with a wire brush to remove the soot. If you are unable to clean it sufficiently or it is broken or has a hole in it, replace it with a new spark arrestor.

12. Flooded DeWalt String Trimmer

I have had customers bring their string trimmer to the repair shop because they can’t get it started. Many times it’s due to a flooded engine which isn’t too serious.

The engine can become flooded when the choke is in the closed position and the starter rope was pulled many times allowing too much gas into the carburetor.

It can also happen with the switch off and the starter rope being pulled multiple times or when the primer bulb is pushed too many times.

Solution: Use the following procedure to “unflood” your string trimmer so the engine gets the correct fuel-to-air ratio required to start and run.

How to Fix a Flooded Engine on a DeWalt String Trimmer

  • Move the choke lever to the run position.
  • Press the throttle trigger lockout and throttle control while pulling the starter rope over and over. This can take anywhere between 5 and 15 pulls before it starts. Your string trimmer engine will sputter first. Continue to pull a few more times and it should start.