Your lawn mower begins to sputter and hesitate as you mow. It seems like it’s not getting gas so you check the fuel tank first only to find you have sufficient fuel. So what is really happening?
A lawn mower will act like it’s running out of gas due to a plugged fuel filter, clogged fuel line, faulty fuel pump, dirty carburetor, plugged gas cap, water in the fuel tank, or old gas.
Work in a well-ventilated area when working with your fuel system. Follow all safety precautions outlined in the mower’s operators manual.
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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.
7 Reasons Your Lawn Mower Acts Like Its Running Out of Gas
Bad or Old Fuel
The root cause of your lawn mower acting like it’s running out of gas is usually due to the quality and age of fuel. Most gas sold today includes ethanol.
This is an alternative fuel made from corn or other high-starch plants to make gas more environmentally friendly. Ethanol may be better for the environment, but it is not good for small engines like the one on your mower.
Ethanol attracts moisture to the fuel. This ethanol and water mixture will prematurely corrode components and leave behind a varnish that gums up the fuel system causing a mower to act like it’s not getting gas.
Because gasoline can begin to break down as quickly as 30 days after purchase, it’s important to use fuel within this timeframe.
If you purchased more fuel than you will use in 30 days, use a fuel additive to like Sea Foam Motor Treatment to stabilize the fuel.
I actually like to add Sea Foam to every tank of fuel as added protection to the fuel system and to reduce moisture.
Solution: Drain your fuel tank using a fuel siphon into an approved fuel container. Fill with fresh fuel that includes a fuel additive like Sea Foam that acts as a fuel cleaner and reduces moisture.
Learn more about the advantages of adding Sea Foam to your fuel here.
Plugged Fuel Filter
The fuel filter strains fuel as it comes out of the fuel tank to keep dirt and other contaminants from entering the fuel system. This filter can become plugged restricting the amount of fuel passing through the filter.
This lack of fuel can be the reason your lawn mower acts like it’s running out of gas.
To avoid clogging the filter, you should replace the filter annually and more often if you find the gas was dirty.
Solution: Replace the fuel filter. Install the new filter with the arrow on the side of the filter housing pointed in the direction of the fuel flow. This means the arrow should be pointed toward the carburetor and away from the fuel tank.
Clogged Fuel Lines
Old fuel can leave behind gummy deposits in the fuel lines. These deposits narrow the opening in the fuel line preventing a good flow of fuel.
To identify a clogged line, you will have to check each section of the fuel line to isolate the area of the clog.
Solution: Use your fuel shut-off valve, located at the bottom of your fuel tank, to start and stop fuel flow. Don’t worry if you can’t find a fuel shut-off valve. Not every mower has one.
If your mower doesn’t use a fuel shut-off valve, use hose pinch pliers to crimp your fuel lines to stop the fuel from flowing.
Find & remove a restriction in a fuel line:
- Work on one section of the fuel line at a time. I start with the line furthest from the tank because if you’re getting good flow there, you don’t have to check the other sections of the line.
- Stop the fuel flow using the fuel shut-off valve or pinch pliers.
- Remove the end of the fuel line furthest from the fuel tank and place it in a container. Make sure the container is placed lower than the tank so the fuel can run downhill.
- Restart the fuel flow.
- If you are not getting good flow into the container, you must remove the restriction in the fuel line. Do this by stopping the fuel flow and removing the fuel line from your mower.
- Spray carburetor cleaner into the hose and blow the line out with compressed air to remove the blockage. Repeat as necessary until the fuel line is open and no longer restricted.
- Reattach the fuel line onto the mower.
- If you are unable to clear the fuel line so fuel can flow freely, replace your fuel line. It’s also a good time to replace your fuel line before it starts leaking if the line is dry and showing signs of cracking as well.
Bad Fuel Pump
You will have a plastic or metal fuel pump on your lawn mower only if the fuel tank sits lower than the carburetor.
A vacuum fuel pump is designed to build pressure off of the crankcase. It uses this pressure to push fuel up to the carburetor.
When the fuel pump has cracks, is damaged or leaks, you must replace your fuel pump. If you don’t notice any damage or leaking of the fuel pump, it’s time to troubleshoot the pump to ensure it is working correctly.
Solution: Confirm the fuel pump is functioning properly by, first, checking to make sure you are receiving fuel flow to the pump. You may have already checked this in the previous step when you checked your fuel lines for blockage.
Once you have confirmed you are getting sufficient fuel to the fuel pump, remove the fuel line from the carburetor and place it in a container.
Next, start your fuel flow and start your mower. You should see a steady or pulsating stream of fuel flowing out of the fuel line signifying your fuel pump is working correctly.
Replace a bad or damaged fuel pump that is not pumping a stream of fuel out of the pump.
The carburetor regulates the air and fuel mixture allowed into the cylinder to create a combustion. You will find your carburetor mounted to the top or side of the engine block. It is usually below or behind your air filter.
When the carburetor is dirty, the components of your carburetor, including the fuel jet, can become clogged or stuck preventing your mower’s engine from receiving fuel.
Solution: Remove your air filter and spray carburetor cleaner into the air intake. I prefer carburetor cleaner over starter fluid because starter fluid is a dry chemical.
Start your engine to see if it will run. If your lawn mower starts and runs fine and then begins to run sluggish like it’s not getting fuel, you will need to clean the carburetor.
Bad Fuel Cap
The fuel tank must be able to vent so the pressure inside the tank equals the atmospheric pressure outside of the tank. When the vent is plugged, the tank will form a vacuum and starve the mower of fuel.
The vent on most lawn mowers is located in the fuel cap. The cap allows air to pass through the cap into the fuel tank.
Solution: Run your mower with and without the fuel cap to confirm whether or not you have a bad fuel cap problem.
If your mower starts and runs well without the fuel cap and then sputters and acts like it’s not getting fuel after you reinstall the fuel cap and allow the mower to run for a while, you may have a problem with your fuel cap.
Water in the Fuel Tank
If you left your mower in the rain or it has been in storage for a long time, you may have water in the fuel tank that can cause it to act like it’s not getting gas. Water is not combustible.
Because water is heavier than gas, it will sink to the bottom of the fuel tank. You may be able to see water using a flashlight.
Solution: Once you discover water in the fuel tank, you must drain the tank. You will also need to drain the fuel out of the fuel lines and the carburetor bowl.
You can use air to dry out and remove any water remaining after draining the fuel lines and tank. I choose to fill a mower with fresh gas that includes a fuel additive like Sea Foam to reduce moisture.
Once you add this gas and Sea Foam mix to the fuel tank. Start and allow the mower to run to get the fresh gas and stabilizer mix to run through the mower.
Running the right kind of gas through your lawn mower and always running fresh gas through your mower will reduce the amount of clogging and damage in your fuel system.
When the mower isn’t getting fuel, check your fuel system components including your filter, lines, pump, and carburetor.
Still Having Problems with Your Lawn Mower?
Lawn mower ownership doesn’t come without its frustrations. Own a mower long enough, you are bound to run into many lawn mower problems including starting, smoking, leaking, cutting, and overheating.
For mower troubleshooting, check out my guide Common Lawn Mower Problems: Solved.