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SOLVED! 12 Reasons a Toro String Trimmer Won’t Start

Your string trimmer, weed eater, or whatever you call it is a tool to help you complete the appearance of your well-manicured lawn. It’s great to trim around the landscaping, trees, and water features. That is until is just stops working.

A Toro string trimmer won’t start when the engine isn’t getting sufficient air, fuel, and spark.

Stay safe and follow the safety precautions listed in your Toro operator’s manual. This includes removing the spark plug boot before making repairs.

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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 Toro String Trimmer Will Not Start

1. Old Fuel

Allowing fuel to sit in your Toro string trimmer can have negative effects. That’s because old fuel can cause corrosion and fuel restrictions.

This is largely due to the ethanol used in most gas sold today. Ethanol is an alternative fuel that naturally attracts water from the air.

The ethanol and water mixture separate from the gas leaving behind varnish and deposits that can cause clogs. The clogs may keep fuel from getting to the engine keeping it from starting.

Because gasoline begins to break down as soon as 30 days after purchase, it’s best to only purchase the amount of fuel you are able to consume within 30 days.

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. Some 2-cycle oils will include a fuel stabilizer. You can also use a product like Sea Foam Motor Treatment.

Toro 2-cycle strimmers require a gas and oil mixture at a 50:1 ratio.

SOLUTION: Drain any old fuel remaining in your string trimmer and fill it with fresh fuel. Add a fuel stabilizer like Sea Foam Motor Treatment or STA-BIL to stabilize the fuel and reduce moisture.

String trimmer parts location

2. Incorrect 2-Cycle Oil Mix

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

A 2-cycle Toro 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 Toro string trimmer, use unleaded gasoline with a minimum octane rating of 87 (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 Toro All Weather 2-Cycle Oil or I like this 2-cycle oil by Kawasaki.

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 Toro 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. I like to stay with OEM brands. Some aftermarket brands don’t offer the same performance.

Toro 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
Toro 2-Cycle String Trimmer Gas-to-Oil Mix

3. Plugged Air Filter in a Toro String Trimmer

An air filter must be used on your string trimmer to keep dirt from causing engine wear. Always run your string trimmer with a clean filter installed to avoid engine damage and voiding the warranty.

The air filter must be checked and cleaned or replaced regularly to keep it in good condition. If you don’t, the filter can be so plugged with dirt that the engine won’t start because it isn’t getting sufficient air required to ignition.

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. You may think you can resolve this by removing the filter so you don’t run into this plugged air filter problem.

I recommend the average homeowner should replace the air filter annually and clean it several times throughout the lawn care season.

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

The spark plug is a maintenance item that should be replaced each year to keep your string trimmer running at its best. The spark plug will become dirty over time with a buildup of carbon. This can cause the plug to misfire having intermittent starting problems.

Other items to look for is cracked porcelain or burnt electrode; a loose spark plug wire; and an incorrect spark plug gap. These items can also cause a starting issue with your Toro.

SOLUTION: 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.

Make sure your spark plug is gapped to the manufacturer’s specification and the spark plug wire (boot) is securely attached.

5. Dirty Carburetor

The carburetor regulates the amount of fuel that is mixed with air to create combustion in the cylinder. Old fuel will gum 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 Toro 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.

6. Plugged Fuel Filter

You will find the fuel filter inside the fuel tank. It’s a small cylinder-shaped filter attached to the fuel line.

Its purpose is to strain the fuel as it enters the fuel system to keep dirt and debris out. Again, dirt can cause wear on the engine potentially damaging it beyond repair.

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 hook the fuel line and pull the filter 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.

7. Bad Primer Bulb

When the primer bulb is cracked or punctured, fuel won’t move to the carburetor when you depress the bulb.

SOLUTION: Replace with a new primer bulb.

8. Fuel Line Blocked

Old fuel may leave behind gummy deposits in the fuel line that will keep the carburetor from getting fuel.

SOLUTION: Replace a fuel line on your Toro 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 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. On a Toro string trimmer, the fuel tank vent is most likely built into the fuel cap.

10. Bad Recoil Starter

Your Toro 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. Plugged Spark Arrestor

You will find a spark arrestor in your Toro string trimmer. The spark arrestor is a small screen installed on the muffler to keep hot exhaust materials from shooting out of the trimmer.

This is a safety feature to prevent injury or fires from this hot material. The spark arrestor must be checked and cleaned through the season so it does not plug and cause the engine to run rough or not even start.

SOLUTION: Disconnect the spark plug boot. Make sure the 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 Engine

You may have flooded the engine and the trimmer will no longer start. Don’t worry. This is easily fixed.

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 Toro String Trimmer

  • Move the choke lever to the RUN 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 string trimmer engine will sputter first. Continue to pull a few more times and it should start.