Have a lawn mower that won’t start? Even though it’s common to run into a starting problem at some point during the life of a mower, it’s frustrating when it happens to you. Finding and fixing the reason your mower isn’t receiving the air, fuel, and spark it requires to run will get your mower up and running again.
A Lawn Boy mower won’t start when it doesn’t get a good supply of fuel due to a lack of fuel, old fuel, clogged fuel line, bad fuel pump, plugged fuel filter, bad fuel cap, or dirty carburetor. A Lawn Boy also won’t start when the air filter is plugged; the spark plug is bad; or the battery, starter solenoid, or ignition coil is bad.
Keep reading for additional items that can cause your Lawn Boy to fail to start.
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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 Lawn Boy Mower Won’t Start
Empty Fuel Tank
Your Lawn Boy mower requires gasoline to run. You know that already. I mention it because you may have simply forgotten to check the gas tank when looking for other reasons your mower won’t start. You may have also developed a gas leak causing your tank to empty sooner than usual.
Solution: Check the fuel tank and refill it with fresh fuel when it is low or empty. Note: For a 2-cycle engine, fill with a gas and oil mix. Read more about the correct gas in “This is the Kind of Gas to Use in Your Lawn Boy Mower“.
Fuel Valve is in the Off Position
Fuel valves are often used to shut off the fuel supply while transporting the mower or storing it for long periods.
Check to make sure the fuel shut-off valve is in the open position allowing fuel to flow out of the tank and through the fuel lines. Your Lawn Boy won’t start and run without the fuel supply turned on.
Solution: Turn on the fuel valve so gas can flow out of the tank. Note: Not all mowers have a shut-off valve so don’t worry if you can’t find one.
Bad or Old Fuel
Gasoline doesn’t age well. It can begin breaking down and becoming less effective as soon as 30 days after purchase. Because of this, it’s important to purchase fresh gasoline and use it within this time.
If you are unable to consume all of the fuel, make sure you add a fuel additive to stabilize the gas to minimize negative effects on your fuel system and engine.
Ethanol, an alternative fuel found in most types of gasoline today, is not good for small engines like those used on a Lawn Boy mower. It attracts moisture that is corrosive to the fuel components.
Additionally, the ethanol and water mix can leave behind a gummy solution that clogs the fuel system. This will prevent the engine from getting the fuel it requires to start.
Solution: Drain old fuel from your Lawn Boy mower using a fuel siphon pump. Add fresh fuel with an ethanol content no greater than 10% and a minimum octane rating of 87 to a 4-stroke engine.
Older Lawn Boy mowers may use a 2-cycle engine which requires a gas and oil mix. To identify the type of engine you have and the type of fuel you need, read this guide.
I recommend adding a fuel additive like Sea Foam Motor Treatment to stabilize the fuel, reduce moisture and help clean the fuel system. Learn more about the positive effects of using Sea Foam here.
Bad Gas Cap
A Lawn Boy mower gas cap is vented to allow air to pass through the cap. When the vent in the cap becomes clogged, your fuel tank will not be able to vent causing it to form a vacuum restricting fuel from flowing out of the tank.
Run your mower with and without the fuel cap. If it starts without the cap but eventually shuts down after replacing the fuel cap, you may have a cap that cannot vent.
Solution: You can attempt to clean your cap to remove the cap or replace it with a new Lawn Boy gas cap.
Lawn Boy push mowers use a blade control bar as a safety feature on the mower. This is a safety feature that will prevent the mower from running when the operator is no longer present.
The blade control bar must be pulled back and held against the handlebar to start and run the mower.
Make sure the blade bar is held against the handlebar while turning the ignition key on an electric start mower or pulling the recoil on a manual start mower. When the blade control lever is released, the engine will stop and the blades will not continue to turn.
Solution: Make sure you are using the right starting procedures for your mower. Check the safety switch to ensure it is working correctly.
Plugged Fuel Filter
A fuel filter is used to protect your fuel system and engine from damage resulting from dirt and debris in the fuel. The filter strains the fuel to keep these contaminants out. When the filter isn’t changed regularly or the fuel is very dirty, it can become plugged preventing fuel from passing through the filter.
Solution: Install a new filter with the arrow found on the side of your filter pointing in the direction of the mower’s fuel flow. The arrow should be pointed toward your carburetor and away from the fuel tank.
Blocked Fuel Line
Dirt and deposits formed from running old fuel can cause a blockage in the fuel line. Check the fuel line by stopping your fuel flow using the fuel shut-off valve. If your Lawn Boy mower doesn’t have a valve, crimp your fuel line to stop flow using pinch pliers.
Remove the end of a section of the hose furthest from your fuel tank and place it in a container. Start your fuel flow and make sure you are getting fuel into the container. The container must be placed lower than the fuel tank. Fuel cannot run uphill.
Solution: If you don’t get a good flow of fuel out of the fuel line into the container, stop your fuel flow and remove the fuel line from your mower. Spray carburetor cleaner in the line to loosen up the clog.
Use compressed air to blow through the line to remove the blockage. Repeat as necessary. If you cannot free the line of the clog, replace it with a new fuel line.
The carburetor’s function is to regulate the amount of gas mixed with air to form combustion in the cylinder.
When the carburetor is dirty and gums up from old fuel, components in the carburetor no longer function properly. The carburetor may not allow the release of gas required to start your Lawn Boy mower.
If you have verified you are getting fuel to the carburetor, remove the air filter and spray carburetor cleaner into the air intake. Start your mower. If it starts, runs, and then shuts down, you may have a dirty carburetor that must be cleaned to remove restrictions and stuck parts.
Solution: Take your carburetor apart to clean it. You can find instructions for cleaning your carburetor here.
Plugged Air Filter
The air filter is an important maintenance part of your Lawn Boy mower. It offers protection to the engine and keeps dirt and debris from getting sucked into the air intake. The air filter must be kept clean and in good condition so it performs at its best.
A plugged air filter can restrict airflow to the mower and not allow the engine to get the air it needs to form combustion. It is best practice to replace your air filter annually. Check and clean your air filter several times throughout the mowing season.
Solution: Remove the air filter from the air filter housing. Be careful not to let dirt fall into the air intake. Wipe out any dirt that is sitting in the housing. Follow the steps below for your type of filter:
Clean a Lawn Boy paper air filter
- Tap your paper air filter against a solid surface to loosen the dirt and allow it to fall out of the filter.
- Hold the filter up to a light source. If you can see light shine through the filter, go ahead and reuse it. If you can’t or if the filter is covered in oil, replace it with a new filter.
- Install the filter.
- Attach the air filter cover.
Clean a Lawn Boy foam air filter
- Check the condition of your foam filter. If it is dry, brittle, torn, or damaged purchase a new filter.
- Wash a good filter with a mild dish detergent and water to remove dirt.
- Rinse the filter until all soap is removed and the water runs clear.
- Lay the filter flat and allow it to dry.
- Once the filter is completely dry, coat the filter with foam filter oil. This is to help trap dirt.
- Install the filter.
- Attach the air filter cover.
Bad or Improperly Gapped Spark Plug
A spark plug can be faulty and fouled when the tip is dirty, the porcelain is cracked or the electrode is burnt.
Additionally, a spark plug must be properly gapped following the manufacturer’s specifications as found in your Lawn Boy mower operator’s manual. Starting problems can be caused by a spark plug that is gapped incorrectly or loose spark plug wires.
Solution: Install a new spark ensuring it is gapped correctly and the spark plug wire is securely attached. If you choose to attempt to clean the spark plug, use a wire brush to remove carbon deposits. If your spark plug tip is very dark in color or damaged, you must replace your spark plug.
Bad Battery or Blown Fuse
If you use a Lawn Boy mower with an electric start, the battery may be bad or it might not have a sufficient charge to start your mower. Try to start your mower with the manual recoil. If the mower starts with the recoil, you have a problem with the electric start.
Solution: Charge your battery using the battery charger. Plug the charger into the port connector on the handle closest to the battery. Charge by plugging it into a 120-volt outlet.
If the battery fails to charge, check the fuse. When the fuse is bad, the battery will not charge and the electric start will not work. If the fuse is fine and your battery won’t charge, replace the battery.
If it still doesn’t charge, have your Lawn mower looked at by an experienced mechanic to troubleshoot additional charging problems.
Bad Ignition Switch
You may have a bad ignition switch. You can test it and replace if it is bad.
Bad Ignition Coil
Before checking for a bad ignition coil, make sure your spark plug is in good condition. The ignition coil provides voltage to the spark plug so it can start the engine. If the spark plug isn’t able to fire, the engine will not start.
Solution: Check the continuity of the ignition coil using an ohm meter. If you find a break in the continuity, replace the ignition coil.
The recoil on your mower may no longer be able to start your mower. A rope on the recoil can become unstrung or you may find you have a broken pulley, springs, or clips in your recoil that need to be repaired.
Solution: Sometimes, restringing the recoil is all you need. Other times you will have to replace broken parts in your recoil. Before doing this, price out a full recoil replacement.
Depending on the price difference, it may be better to replace the recoil assembly over tearing it down and replacing broken components.
Bad Starter Solenoid
The solenoid on a Lawn Boy mower is an electromagnetic switch that acts like an on-off switch that actuates the starter motor to turn over the engine.
If you hear a click or hum when turning the ignition key or the wires attached to your solenoid get hot and begin to smoke, you need to test the solenoid.
Solution: I have listed steps to check your solenoid here. Replace your starter solenoid if you find it to be bad.