Your lawn mower isn’t running and you’ve come to the conclusion you aren’t getting fuel to the carburetor.
The carburetor regulates the amount of fuel mixed with air to form combustion in the engine. Without fuel, you’re not going to be getting any mowing done until the fuel supply issue is fixed.
A lawn mower carburetor will not get fuel when old gas corrodes fuel components and leaves gummy deposits restricting the fuel system.
A plugged fuel filter; clogged or kinked fuel lines; a faulty fuel pump; a stuck carburetor float and float needle; or a bad gas cap can result in a lawn mower carburetor not getting fuel.
Before working on your lawn mower, make sure you are in a well-ventilated area. Follow all safety precautions outlined in your operator’s manual. Take caution when working around a hot engine.
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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 a Lawn Mower Carburetor Isn’t Getting Fuel
First, check the fuel in your lawn mower. Running old gasoline in the mower can cause fuel restrictions keeping your mower from getting gas.
Make sure you are running fresh gasoline so, after you fix your fuel flow problem, you don’t develop restrictions from continuing to run old gas.
Most types of gasoline contain ethanol, a corn-based fuel, to make gas more environmentally friendly. Ethanol naturally attracts moisture from the air.
The mixture of ethanol and water will cause sticky deposits to form causing blockages in the fuel system. This mixture can also cause your fuel components to fail prematurely.
Because gas can break down as quickly as 30 days after you buy it, it’s not only important to use the right type of fuel, but it’s also necessary to consume the fuel you purchase in this time frame.
Read more about the right kind of gas to use in your lawn mower along with how to store it here.
FIX: Use a siphon pump to drain the old fuel from your tank. Collect the fuel in an approved fuel container so you can later recycle it.
Add fresh fuel along with a fuel additive to stabilize the fuel, reduce moisture and clean the fuel system. I use Sea Foam Motor Treatment in my lawn mower. You can read more about the advantages of Sea Foam here.
Plugged Fuel Filter
Dirt in the fuel system can clog the fuel system and damage fuel components.
To strain any dirt, sediment, or other contaminants to keep them from entering the fuel system, a fuel filter is installed. Most lawn mowers use an inline fuel filter. A fuel line attaches to each end of the filter.
If you are running very dirty fuel or if you haven’t changed your fuel filter annually, the fuel filter can become plugged. When this happens, fuel cannot pass through the filter and to your carburetor.
FIX: Replace a plugged air filter. You will find an arrow on the side of the filter. The new filter must be installed with this arrow pointing in the direction of your fuel flow. The arrow should be pointed toward the carburetor and away from the fuel tank.
Clogged Fuel Lines
Gummy deposits left behind from running old fuel can prevent fuel from flowing through the fuel lines. To find a clog in the fuel line, you will need to check each section of the fuel line by stopping and starting your fuel flow to check for good flow from each section of the line.
You can control the fuel flow using the fuel shut-off valve located at the bottom of the gas tank. If your mower doesn’t have a shut-off valve, pinch pliers also work to crimp the fuel line to stop the flow.
FIX: Once you find a section of the line that is clogged, remove the line from your mower. Spray carburetor cleaner into the line to help loosen the clog. Blow out the line with compressed air. Repeat until you dislodge the clog and open the line.
If you are unable to unclog the line or the fuel line is dry and cracked, it’s time to replace your fuel line.
Bad Fuel Pump
Most gas-powered lawn mowers use a vacuum fuel pump when the carburetor sits higher than the fuel tank. This type of pump builds pressure off the crankcase. It moves fuel to the carburetor because fuel won’t run uphill without it.
When the fuel pump cracks or fails to work correctly you will have to replace it. If you don’t see physical cracks or fuel leaking, you must take some troubleshooting steps to isolate the problem to your fuel pump.
FIX: Before you check your fuel pump, check to make sure you are getting fuel to the fuel pump. You may have completed this step already if you checked your fuel lines and filter for blockages, but if you didn’t, you need to start here.
Stop your fuel flow. Remove the fuel line off the inlet port of your fuel pump. Place the line in a container placed lower than the fuel tank and restart your fuel flow.
If you are getting fuel out of the line and into the container, you have confirmed you have flow. If not, you need to find the blockage that may be in your fuel lines or fuel filter.
Once you have confirmed fuel flow to the pump, reattach the fuel line to the inlet port. Remove the fuel line from the carburetor and place it in a container. Check your pump is working correctly by starting your fuel flow and starting your mower.
You should have a steady or pulsating flow of fuel coming out of the fuel line. If you do not, you need to replace your fuel pump.
Stuck Float or Float Needle
The carburetor won’t get fuel when the float or float needle is stuck and won’t allow fuel to flow into the carburetor bowl. The float and float needle are responsible for regulating the amount of fuel in the bowl.
A float and float needle can become stuck and fail to allow gas into the carburetor bowl. You can attempt to temporarily fix this by tapping on the carburetor with a rubber mallet or the rubber end of a hammer to “unstick” the float needle.
This will work for a time or two, however, the carburetor will have to be disassembled, cleaned, and repaired.
FIX: Take your carburetor apart when you find a stuck float or float needle to determine the actual cause of the failure. You may be able to clean the carburetor to keep the float from sticking.
You may also have to rebuild or replace it to get the carburetor to work right. Read the steps to clean your carburetor in this article.
Bad Gas Cap
Air passes through the vent in a lawn mower gas cap. When this vent becomes plugged, the gas tank acts like a vacuum preventing fuel from leaving the fuel tank.
You may be able to determine whether your fuel cap is clogged by starting your mower and allowing it to run with and without a cap.
If the engine runs okay without the fuel cap, but eventually shuts off or begins to run sluggish with the fuel cap in place, you may have a plugged fuel cap.
FIX: You can attempt to clean your fuel cap to unclog the vent. If this doesn’t work, purchase a new gas 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.