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Reasons a Weed Eater Lawn Mower Won’t Start: FIXED!

Your lawn mower does its job to keep your home’s exterior appear well-maintained. You rely on it to keep working so you don’t get behind on your lawn care. However, no matter what brand mower you own, when you own it long enough you’re bound to run into starting problems.

A Weed Eater lawn mower won’t start when the engine isn’t getting sufficient air, fuel and spark. This is caused by a plugged air filter, old fuel, plugged fuel filter, clogged fuel line, bad fuel pump, faulty ignition coil, bad spark plug, bad safety switch or incorrect mower operation.

Before working on your lawn mower, follow all safety precautions provided in your operators manual. This includes wearing safety gear and letting your mower’s engine cool to avoid burns.

Weed Eater Lawn Mower Won't Start

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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, knowledge or are not in the condition to perform the repair safely.

This is Why Your Weed Eater Lawn Mower Won’t Start

No Gas Will Cause Your Weed Eater Mower Not to Start

Everyone knows a gas-powered Weed Eater lawn mower won’t start when there isn’t gas in the tank. I only mention this because you may have simply forgot to check the fuel level out of frustration. You may also have a broken fuel gauge or may have developed a fuel leak causing you to run out of fuel sooner than usual.

Solution: Check the fuel level. Check for a broke fuel gauge or a fuel leak and repair them if you find a problem. Fill your gas-powered Weed Eater mower with fresh gasoline that has a minimum octane rating of 87 or higher. Use the right kind of gas with an ethanol level no greater than 10%.  

If your Weed Eater lawn mower uses a 2-cycle engine, you must mix a 2-cycle oil with the gas before adding it to the fuel tank.

Bad or Old Fuel Will Cause Your Weed Eater Mower Not to Start

Gas that has been left sitting in the fuel tank during the winter season or for periods greater than 30 days can breakdown and become less effective. The gas can leave behind a varnish and sticky deposits that can clog the fuel system.

This will cause the engine to not start because it isn’t getting sufficient fuel to form a combustion. Most gas available at fuel stations today contain ethanol.

Ethanol is an alternative fuel, often made from corn, that is added to make gas more environmentally friendly. While ethanol is okay to use in most vehicles, it will have negative effects on your Weed Eater lawn mower engine.

Ethanol attracts moisture from the air introducing water to the fuel system which can cause premature corrosion in the mower. This ethanol and moisture mixture will end up separating from the gas over time and sink to the bottom of the fuel tank.

The engine will run extremely hot when this mixture is run through the engine. Because of the bad effects that can result from using gasoline that contains ethanol, it’s important to never use gas with a high level of ethanol.

Weed Eaters require an unleaded gasoline with a minimum octane rating of 87 and a maximum ethanol content of 10%.

This is gas sold as “regular” or “E10” gas. Straight gas is used in a Weed Eater 4-stage engine, while a gas and oil mix is used in a 2-cycle engine. If you are unsure of the type of engine your Weed Eater uses, refer to your operator’s manual.

  • 4-stage (4-cycle) Weed Eater lawn mower engine:
    A 4-stage engine will have a separate fill ports, one for engine oil and one for gasoline. Fill the fuel tank with fresh unleaded gasoline.
  • 2-cycle Weed Eater lawn mower engine:
    Some Weed Eater lawn mowers will use a 2-cycle engine. This type of engine will have one fill port for a gas and oil mix. Weed Eater lawn mowers with 2-cycle engines require a gas to oil mix of 40:1. Always confirm the mixture ratio by consulting your operators manual as the requirements can change with engine models.

    Never run straight gas through a 2-cycle engine as this will damage the engine and certainly ruin your engine. Use a good 2-cycle engine oil mixed with gasoline. 2-cycle engine oil is different than engine oil.

More fuel stations are adding E15 and E85 fuels which contain up to 15% and 85% ethanol. Stay away from these fuels. If possible, it is best to use an ethanol-free fuel.

However, this is a more costly option. You can find fuel locations that offer ethanol-free fuel near you using the website puregas.org. You can also purchase it in canisters at your local hardware store or online.

Solution: Remove the old fuel using a fuel siphon pump and add fresh fuel. Add a fuel additive like Sea Foam Motor Treatment or STA-BIL to stabilize the gas, clean the fuel system and reduce moisture. Read more about why I use Sea Foam in my lawn mower here.

When you purchase more fuel than you are able to use within 30 days, add fuel stabilizer to make your gas last a little longer without breaking down and minimize problems due to old fuel.

Bad Gas Cap Will Cause Your Weed Eater Mower Not to Start

The fuel cap on your Weed Eater lawn mower is designed to vent. The vent can become clogged preventing air from passing through the cap and into the tank to equalize the air pressure. A plugged vent in a fuel cap will create a vacuum in the tank and won’t allow fuel to flow out of it.

Without fuel, your Weed Eater mower won’t start. To identify a bad fuel cap, loosen the cap or remove it to allow air into the fuel tank. The mower should start now if a lack of air in the tank was causing the problem. Be careful and don’t allow debris to fall inside the tank.

To further confirm the fuel cap is the problem, reinstall the fuel cap. Continue to allow the mower to run. If your mower once again shuts down and doesn’t start again until you loosen the fuel cap, it’s time to replace the gas cap with a new one.

Solution: Replace s broken or plugged cap with a new fuel cap.

Bad Spark Plug or Loose Connection Will Cause Your Weed Eater Mower Not to Start

A fouled spark plug covered in carbon buildup can keep your Weed Eater lawn mower from starting. Remove the spark plug and check for a dirty insulator tip, broke porcelain or burnt electrode. If you find any of these conditions, it’s best to replace the spark plug with a new one.

If you find your plug is in good condition and is mildly dirty, clean it with a wire brush before reinstalling. Make sure the gap matches the engine manufacturer’s specification.

Solution: A bad plug can cause the mower to misfire and run sluggish. Replace a bad plug with a new spark plug. Check the gap and securely attach the spark plug wire (boot) to ensure it is making good connection.

Plugged Air Filter Will Cause Your Weed Eater Mower Not to Start

A plugged air filter can keep the engine from getting clean air. It will starve the engine causing the mower not to start. Keeping the air filter clean and free of dirt and debris will reduce significant engine issues including overheating.

I suggest replacing the air filter annually. Clean it several times during the lawn mowing season to help protect your engine and allow it to run at its best.

Solution: Remove your air filter and inspect it. Clean the filter or replace it if necessary using the following steps:

Clean a Weed Eater lawn mower paper air filter:

  • Remove the air filter housing cover.
  • Remove the air filter being careful not to allow dirt to fall into the air intake.
  • Wipe out any dirt that remains in the housing.
  • Tap the plastic or rubber part of the filter against a hard surface to loosen the dirt so it falls out of the filter.
  • Once you have removed as much dirt as possible, hold the filter up to a light source. If you can see light through the paper filter, reuse the filter. If you can’t see light or if it is covered in oil, replace the air filter.
  • Install either a clean reusable filter or a new filter.
  • Reattach the air filter cover.

Clean a Weed Eater lawn mower foam air filter:

  • Remove the air filter housing cover.
  • Remove the air filter being careful not to allow dirt to fall into the air intake.
  • Wipe out any dirt that remains in the housing.
  • Reuse the filter if it is in good condition and not brittle, forming dark spots or have tears in the filter. Purchase a new foam air filter if you find any of these conditions.
  • Wash a filter that is able to be reused. Use a mild dish soap and water to remove dirt. Rinse until clear.
  • Lay flat to dry.
  • Once completely dry, coat with a foam filter oil and replace in the filter housing.
  • Reattach the cover.

Plugged Fuel Filter Will Cause Your Weed Eater Mower Not to Start

The fuel filter prevents dirt and debris into the engine by straining the fuel. When the filter isn’t changed regularly, the filter can become plugged keeping fuel from passing through the filter.

Solution: If you are not getting fuel flowing through the fuel filter, replace the filter. You will find an arrow on the new filter that must be installed with the arrow pointing in the direction of the fuel flow.

Clogged Fuel Line Will Cause Your Weed Eater Mower Not to Start

Old fuel and dirt leave deposits that can clog your Weed Eater mower’s fuel line. To find a clogged fuel line, check each section of fuel line while starting and stopping the fuel flow. For more detailed instructions on how to identify a clogged line, read “This is Why Your Lawn Mower Isn’t Getting Fuel“.

Solution: Remove the fuel line, spray carb cleaner into the tube and use compressed air to blow air through the tube until the line is free of dirt and gummy residue. You can also replace with new fuel line

Bad Fuel Pump Will Cause Your Weed Eater Mower Not to Start

The fuel pump exists to move fuel to the carburetor. Not all Weed Eater mowers use a fuel pump. Your mower will have a fuel pump when the fuel tank sits below the carburetor and a pump is require to move the fuel uphill through the fuel line.

A fuel pump, just like any other mechanical part, can fail over time. A likely cause is due to wear and old fuel deteriorating the pump components.

Solution: To identify a failing fuel pump, first, inspect your vacuum fuel pump for cracks. If you see fuel outside of the fuel pump or cracks in pump, the pump must be replaced. Make sure you are getting fuel to the pump and then proceed with the following instructions to check the pump.

Use the fuel shut-off valve or pinch pliers to stop fuel flow. Remove the fuel line from the carburetor and place in a container to collect fuel. Start your fuel flow and start the mower. Watch the flow of fuel into the container.

If you have a steady or pulsating flow of fuel coming out of the fuel line your fuel pump is most likely fine. If you aren’t getting good fuel flow, replace the fuel pump.

Clogged & Dirty Carburetor Will Cause Your Weed Eater Mower Not to Start

The function of the carburetor is to regulate the right amount of gas with the right amount of air so your engine can create a combustion allowing the mower to start and run. Carburetors can get crusty buildup and gummy deposits from using old fuel containing ethanol.

When the carburetor is no longer to regulate the fuel your engine receives, your Weed Eater engine will run rough or it may not even start at all.

Solution: If you are somewhat mechanical, you can try to clean the carburetor yourself, otherwise bring it to your lawn mower repair shop. You can find steps for cleaning your carburetor in this article

You may choose to replace the carburetor if it appears to be in very bad condition. 

Bad Battery or Loose Terminals Will Cause Your Weed Eater Mower Not to Start

Your Weed Eater lawn mower requires a charged battery in order to start. If your cables happen to be loose or your battery terminals show signs of corrosion, they can cause your mower staring problems.

Solution: Test your battery with a multimeter. You will want a reading at about 12.7 volts. Charge your battery if it is lower than this level. You can find more information on charging your battery here. If your battery does not hold a charge, you will need to replace it with a new battery. 

Bad Safety Switch Will Cause Your Weed Eater Mower Not to Start

Your lawn mower may use several safety switches in its operator’s presence control system. The switches are designed to kill the engine when the operator leaves the seat. A faulty switch may not recognize when the operator is in or out of the seat causing your mower not to start. 

Solution: You can temporarily bypass the safety switch to identify a bad switch. Do not operate a mower without the safety switch installed for your safety. Always have safety switches installed and working on your equipment. Replace a bad switch. 

Bad Ignition Switch Will Cause Your Weed Eater Mower Not to Start

You insert the key into your ignition switch and turn it only to find nothing happens. Your Weed Eater mower does not start. The ignition switch can be the culprit. You can use a multimeter to test the ignition switch 

Solution: Replace the switch if bad 

Faulty Ignition Coil Will Cause Your Weed Eater Mower Not to Start

The ignition coil provides voltage to the spark plug so it can fire and start the engine. The engine will not start if the spark plug isn’t able to fire.  

Solution: After you verified your spark plug is in good condition, check the continuity of your ignition coil using an ohm meter. Replace the ignition coil if you find a break in the continuity. 

Bad Starter Solenoid Will Cause Your Weed Eater Mower Not to Start

A lawn mower solenoid is an electromagnetic switch that is like an on-off switch that actuates the starter motor to turn over the engine. A click or hum when turning your ignition key is an indication to check your solenoid.

Another indication your Weed Eater mower solenoid may be bad is when a wire attached to your solenoid gets hot and begins to smoke or melt.

Solution: Test your Weed Eater mower solenoid by following the steps here. Replace your solenoid if it is found to be bad.

Faulty Charging System Will Cause Your Weed Eater Mower Not to Start

If your mower runs with a battery, the charging system can drain the battery and not keep it charged causing your Weed Eater to not start. A bad stator or alternator can be the problem along with several other electrical parts. Read this article to test your charging system here using an ohm meter. 

Solution: If you believe the problem to be in your charging system, I suggest you allow a small engine mechanic to identify which part of the charging system is your problem. Taking a guess at the problem and throwing parts at your mower can get pretty expensive.

Bad Starter Recoil Will Cause Your Weed Eater Mower Not to Start

If you own a Weed Eater push mower without electric start, you will have a recoil to start the engine. The recoil can fail so you are unable to start your mower. 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.

Incorrect Operating Procedure Will Cause Your Weed Eater Mower Not to Start

A Weed Eater mower has safety features that won’t allow your mower to start unless you follow their starting procedures which includes setting your parking brake.

Make sure the choke setting is correct. The choke restricts airflow allowing more fuel into the cylinder to start a cold engine. You must adjust the choke so it doesn’t continue to restrict airflow once the engine is warm or it will shut down.

Solution: Refer to your Weed Eater operating manual to ensure you are operating your lawn mower correctly so you don’t set off the safety features that won’t allow it to start.