Your lawn mower may begin running sluggish, act like it’s going to shut off, or not start. These are all symptoms of a lawn mower not getting fuel. Removing a fuel restriction will get fuel to the engine so it runs at its best.
A lawn mower isn’t getting gas because the fuel is old, the fuel filter is plugged, the fuel lines are clogged, the fuel cap doesn’t vent, the carburetor is dirty, or the fuel pump doesn’t function properly.
Take safety precautions when working with your lawn mower. You can find specific safety guidelines for the mower in your operator’s 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.
6 Reasons Your Lawn Mower Is Not Getting Fuel
Bad or Old Fuel in a Lawn Mower
Fuel starts to lose its combustible properties and breakdown as quickly as 30 days after purchase. Always purchase fresh fuel and consume it right away. The negative effects of old fuel occur in both gasoline and diesel fuel.
Gas for Gas-Powered Lawn Mowers: Using old fuel in your lawn mower can cause problems that will prevent fuel from getting to the engine.
Most types of gasoline sold today include ethanol, a corn-based product to make fuels a little more environmentally friendly. Ethanol naturally attracts moisture which can leave behind a sticky substance that clogs the fuel system.
In addition to creating clogs, the water and ethanol mixture can corrode fuel system components. As gasoline ages, the mixture separates from the gas and sinks to the bottom of the fuel tank. This solution will run hot causing potential damage to the engine.
Use the right gasoline in your gas-powered lawn mower. This is unleaded gasoline with a minimum octane rating of 87 that contains no more than 10% ethanol. Less ethanol in gasoline or even an ethanol-free fuel is best. Read more about the right gas for your lawn mower here.
Diesel for Diesel-Powered Lawn Mowers: Sludge can build up at the bottom of diesel tanks, even those at the fuel station if diesel sits around for long periods. Bad diesel fuel will appear dark in color.
You can also identify old diesel fuel by looking at the fuel filter. The fuel filter will appear dark in color from straining the sludge from the fuel coming out of the mower’s tank.
FIX: When you find old fuel sitting in your lawn mower, drain the fuel tank. A siphon pump works great for this. Make sure you have a fuel container to collect the old fuel. Set aside the old container of fuel to be properly disposed of at a recycling facility.
Refill your fuel tank with fresh fuel. Add a fuel additive to your fuel to stabilize and clean the fuel system. I use a product called Sea Foam Motor Treatment. You can read more about the advantages of Sea Foam here and why I use it in every tank of fuel.
Plugged Fuel Filter on a Lawn Mower
The fuel filter is placed on your lawn mower to filter out dirt and sediments from entering the fuel system and into the engine. When the filter becomes plugged, fuel is no longer able to pass through the filter and through the fuel system.
The filter should be changed at least once a year to keep it in good working order. You may need to change it more frequently when running old or dirty fuel.
FIX: Replace a plugged fuel filter. There should be an arrow on the plastic housing of your fuel filter housing.
Make sure you install the filter correctly with the arrow pointing in the direction of the mower’s fuel flow. This means the arrow should be pointed toward the carburetor and away from the fuel tank.
Clogged Fuel Lines on a Lawn Mower
The sticky deposits that form from the evaporation of ethanol and water can clog the fuel line. To identify a clogged line, you will need to check each section of the line for the restriction. Once you find one, remove the clog by using these steps:
FIX: Remove a lawn mower fuel line clog
- Use the fuel shut-off valve to shut off the fuel supply. You’ll find the valve located at the bottom of your fuel tank.
- If your mower doesn’t have a fuel shut-off valve, use pinch pliers on your line to stop fuel flow.
- Identify a section of the fuel line to check and remove the end of the line from the component (the end furthest from the fuel tank). Place the end into a container to collect fuel.
- Start your fuel flow by opening the fuel shut-off valve or removing the pinch pliers.
- Watch for fuel flow into the container. If you aren’t getting fuel flow, make sure the container is placed lower than the fuel tank because fuel cannot run uphill without the help of a fuel pump. If you still don’t get good fuel flow into the container, you need to remove the clog.
- Shut off the fuel supply and remove the clogged section of the fuel line.
- Spray carburetor cleaner into the line to loosen the restriction.
- Blow compressed air through the line to remove the blockage.
- Repeat spraying carburetor cleaner and blowing compressed air through until the clog is removed.
- If you are unable to remove the clog, replace the line with a new fuel line.
Bad Fuel Pump on a Lawn Mower
You will have a plastic or metal fuel pump on your lawn mower when the fuel tank sits lower than the carburetor. When a fuel pump is needed, most lawn mowers use a vacuum fuel pump. This type of pump builds pressure using the vacuum in the crankcase. It uses this pressure to get fuel to the carburetor.
When the fuel pump has cracks, is damaged, or leaks, you must replace it with a new one. If you don’t notice any damage or leaking of the fuel pump, it’s time to troubleshoot the fuel pump to ensure it is working correctly.
FIX: 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 reviewed this in the previous step if you checked your fuel lines for blockage. If you didn’t, refer to the steps above to check for fuel flow to the pump.
Once you have confirmed you are getting sufficient fuel to the fuel pump, remove the fuel line off 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 pump.
If the mower uses an injection fuel pump, refer to the operator’s manual for manufacturer specifications for the fuel pressure.
Use a fuel pressure gauge to find the pressure reading for the fuel flow out of the pressure line. A fuel pump with a pressure lower than the manufacturer’s specifications must be replaced.
Replace a bad fuel pump that is damaged or is not pumping a stream of fuel out of the pump.
Dirty Carburetor on a Lawn Mower
A gas-powered lawn mower uses a carburetor to regulate the fuel that is mixed with air to form combustion in the engine cylinder. 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 preventing your lawn mower from getting fuel to the cylinder.
First, to help identify a carburetor problem, make sure you are getting fuel to the carburetor. Next, remove your air filter for the air filter housing and spray a little carburetor cleaner into the air intake.
Start your engine to see if it will run. If the mower starts, runs, and then shuts off, you will need to remove your carburetor and take it apart for cleaning.
This is a test to make sure your mower will start using the carburetor cleaner. If it doesn’t, you may have a problem other than a fuel issue.
Refer to my guide on common lawn mower problems for a chart to better identify your mower’s problem.
FIX: Clean the carburetor. Most homeowners can do this if they are a little mechanical and don’t mind working with small parts.
If that’s not you, your local lawn mower repair shop can do this for you. For instructions on cleaning the lawn mower carburetor on your lawn mower, read this article.
Bad Fuel Cap on a Lawn Mower
The fuel tank needs to vent through the fuel cap so it doesn’t act like a vacuum restricting fuel from leaving the fuel tank. When the fuel cap vent is clogged it prevents air from passing through the cap.
To check if your fuel cap is the problem, remove the cap, start, and let your mower run. If it runs fine, reinstall the fuel cap while continuing to allow your mower to run for a while.
If it eventually shuts down with the cap installed but starts and runs again as soon as you remove the cap, you may have a problem with a clogged fuel cap.
FIX: You can attempt to clean your cap to remove the cap. This doesn’t always work and you will have to purchase a new fuel cap.
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.