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13 Reasons a Craftsman String Trimmer Won’t Start (SOLVED)

A Craftsman trimmer won’t start due to a plugged air filter, bad spark plug, dirty carburetor, bad starter recoil, plugged fuel filter, plugged spark arrestor, wrong fuel, wrong oil, old gas, or a flooded engine.

Keep reading for additional items that can cause the starting problem. Follow all safety precautions in your operator’s manual to avoid injury while working on your string trimmer.

This guide references 2-cycle and 4-cycle engines.

Most Craftsman string trimmers on the market today use 2-cycle (2-stage) engines however, the manufacturer has introduced 4-cycle models. Check your operator’s manual if you are unsure what type of engine you are running on your string trimmer.

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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.

Reasons Your Craftsman String Trimmer Will Not Start

When your trimmer doesn’t start, begin by checking the air filter, spark plug, and fuel filter. These are maintenance items that should be replaced at least once a year for the average homeowner.

1. Plugged Air Filter

The air filter is required to keep dirt and debris from entering the air intake causing wear and damage to the engine.

It’s important to keep the filter clean or it can begin to restrict the amount of air that is able to pass through it when it becomes plugged. The Craftsman engine may not get the air it requires to start and run.

Don’t run the string trimmer without a filter just to get the job done while you wait for a new air filter replacement. This can be detrimental to the engine and may result in having to purchase a new Craftsman string trimmer.

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

Where string trimmer parts are located

2. Bad Spark Plug

The spark plug can wear and become dirty with a buildup of carbon. This can cause the plug to misfire and not start.

A loose spark plug wire or an incorrectly gapped plug can also be the cause of a Craftsman’s starting problem.

SOLUTION: Remove the spark plug and inspect its condition. A spark plug that is very dirty, damaged, or worn must be replaced.

You can attempt to clean a dirty spark plug with a wire brush and reuse it. I prefer to replace it. 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.

3. Plugged Fuel Filter

You will find a small cylinder-shaped fuel filter inside the fuel tank. The filter is attached to the fuel line.

Its function is to keep dirt and debris from getting into the fuel system causing fuel restrictions in the fuel line or carburetor. It also keeps dirt from getting to the engine.

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 Craftsman string trimmer starting problem because the engine isn’t getting the amount of 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 hook the fuel line and pull the filter out of the tank.
  • Remove the old filter from the fuel line.
  • Install the new fuel filter.
  • Place the filter back inside the fuel tank and install the fuel cap.

4. Wrong 2-Cycle Oil Mix

Using straight gas in a 2-cycle Craftsman string trimmer will damage the engine and cause it to seize. Adding straight gas to your string trimmer is a quick way to ruin it.

A 2-cycle Craftsman string trimmer uses gas and oil mixed at a ratio of 40:1. 40 parts gas is mixed with 1 part oil.

When creating the oil and gas mixture for your string trimmer, use unleaded gasoline with a minimum octane rating of 89 (mid-grade) and maximum ethanol content of 10%. 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. You can use Craftsman Full Synthetic 2-Cycle Engine Oil.

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 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. You can find ethanol-free premixed fuel at your local hardware store .

2-Cycle Gas to Oil Mix

Mixture1 Gallon Gas2 Gallon Gas2.5 Gallon Gas
40:13.2 oz Oil6.4 oz Oil8.0 oz Oil
Craftsman 2-Cycle String Trimmer Gas to Oil Mix

5. Wrong or Insufficient Engine Oil in a 4-Cycle

If you have a string trimmer with a 4-cycle engine, you will have separate fill ports for the engine oil and gas. Y

Do not mix oil and fuel together for this type of engine. It’s important to use the correct engine oil and the right amount of oil.

Never use 2-cycle engine oil in a 4-cycle string trimmer. Craftsman recommends using SAE30 engine oil in the string trimmer. This engine oil from Kawasaki works well.

Oil is required to keep the engine components lubricated. When the wrong type or not enough oil is used, friction can build in the engine and overheat causing your string trimmer not to start and possibly ruin the engine.

SOLUTION: Drain the engine oil and fill it with the correct oil grade. When running your trimmer in very cold or very hot temperatures, you may have to adjust the viscosity to your ambient temperature.

If you continue to have problems, have a small engine mechanic diagnose the problem and determine whether a cost-effective repair can be made.

4-Cycle String Trimmer Engine Oil

Craftsman 4-Stroke Engine OilSAE30

6. Old Fuel

Old fuel left in a string trimmer won’t only cause fuel restrictions, but it can also damage the carburetor and engine. Gasoline can begin to break down as quickly as 30 days after purchase.

The ethanol found in most types of gasoline attracts moisture from the air. This moisture and ethanol mixture gums up the fuel system and corrodes the components.

Because gasoline can begin to go bad as soon as 30 days after purchase, the fuel must be consumed within this time frame. If you are unable to use it in this amount of time, add a fuel additive to stabilize the fuel so it lasts a little longer.

Always use unleaded gasoline with a minimum octane rating of 89 (mid-grade) and maximum ethanol content of 10% (E10). Never use E15 or E85 in the engine as this will damage the engine and most likely void manufacturer warranties.

SOLUTION: Drain any old fuel remaining in your string trimmer and fill it with fresh fuel. This is an oil and fuel mixture for a 2-cycle engine and unleaded gasoline for a 4-cycle engine.

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

7. Bad Primer Bulb

A cracked 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: Make sure the fuel line is securely attached to the primer bulb. If you find it is damaged or the primer bulb is cracked, replace it with a new one.

8. Fuel Line

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 string trimmer when it is cracked, kinked, or clogged.

9. Plugged Fuel Tank Vent

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 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.

Try to replicate the problem to confirm a plugged vent by tightening the cap and allowing the string trimmer to run. If it eventually dies and fails to start until the cap is loosened, you most likely have a fuel vent problem.

SOLUTION: The tank vents through the fuel cap on a Craftsman string trimmer. Replace the fuel cap.

10. Dirty Carburetor

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

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.

Depending on the model string trimmer you run and the price of a carburetor, it may be best to invest in a new string trimmer rather than put money towards replacing a carburetor on an old trimmer.

11. Bad Recoil Starter

Your 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.

12. Bad Spark Arrestor

You will find a spark arrestor in your 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.

13. Flooded

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 String Trimmer

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