The smell of gas in the storage shed or burnt marks left on the lawn are clues that your push mower is leaking fuel. While it can sometimes be hard to find a fuel leak because gas will evaporate leaving no wet signs on the mower, there are not too many places you’ll have to look before you find the leak.
A push mower can begin leaking gas from the carburetor due to a gasket failure or stuck carburetor components. It can also leak from the fuel shut-off valve, fuel filter, fuel lines, fuel tank, or gas cap.
Before working on a push mower with a fuel leak, make sure you are working in a well-ventilated area. Gas fumes can be harmful. Follow the safety procedures outlined in your operator’s manual to prevent any injuries.
7 Places a Push Mower is Leaking Gas
Carburetor on a Push Mower is Leaking Gas
Your carburetor is a good place to start looking for a fuel leak on your push mower. Carburetors get dirty with gummy and crusty buildups that can cause the parts in your carb to not function correctly.
This is the place fuel is stored after it leaves your gas tank. When parts get stuck or the gasket fails, your push mower will begin leaking gas.
Gasket failure in the carburetor bowl
The first place to check on your carburetor for a leak is the gasket on the carburetor bowl. It’s common for this gasket to become hard and brittle over time due to the location of the gasket.
It’s located right next to the engine so it heats up when the engine runs and cools down when it is not in use. This constant heating and cooling put a lot of stress on the gasket causing it to lose its sealing ability.
The gasket is located between the carburetor bowl and the carburetor. It kind of looks like a rubber band. If you find a leak in this area, you will have to replace the gasket. This is a pretty simple procedure.
You will need to buy a replacement gasket. To find a good replacement, you’ll need to locate the model and spec number from the engine. Don’t confuse this with the model and a serial number of the lawn mower.
Steps to replace the carburetor bowl gasket:
- Shut off the fuel supply using the fuel shut-off valve located at the bottom of your fuel tank. You can also use pinch pliers to crimp the fuel line to stop the flow.
- Wipe the outside of the carburetor so you don’t allow any dirt to enter the carburetor while removing the bowl.
- Have a rag available to collect any fuel remaining in the bowl.
- Remove the screw at the bottom of the carburetor bowl and remove the bowl.
- Remove the old gasket and replace it with the new gasket.
- Reinstall the carburetor bowl.
- Reinstall the screw to hold the bowl and carburetor together.
- Wipe down the carburetor again to remove any spilled fuel
- Turn on the fuel supply and check for additional leaking from the carburetor.
Next, look for a fuel leak near the air intake port. When you find a leak in this area, you could have a stuck float that can no longer regulate fuel flow into the bowl. Fuel keeps flowing into the carburetor bowl and then overflows out of the carb when you have a stuck float.
Take your carburetor apart when you find a stuck float 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.
Stuck float needle
The last thing you should check on your carburetor is the float needle. The float needle works in conjunction with the float to keep gas flowing into the carburetor bowl. If the needle gets stuck, it will need to be repaired.
You will have to take your carburetor apart to fix the float or you can take it to your local small engine mechanic to have the carburetor rebuilt.
Some push mower owners tap on their carburetor gently with the rubber handle on their hammer or with a rubber mallet to free the needle. This does work a time or two, but it is only a temporary fix.
Cracked or Soft Fuel Filter
Gasoline today can cause plastics to degrade which can cause your fuel filter to become soft and leak at the seams. A fuel filter that is leaking or one that has been cracked must be replaced with a new one.
Be careful when removing the ends of the inline filter from your fuel lines as the plastic can become soft and break off. Don’t be alarmed if you don’t find one on your mower. Not all push mower manufacturers place a fuel filter on the mower.
The fuel filter’s purpose is to strain dirt and other contaminants from the fuel after it comes out of the tank and before it enters the rest of the fuel system and engine. If your mower doesn’t come with a fuel filter, you can install one.
The type of fuel you use in your push mower and how you store it can affect the fuel system. Read more about the effects of ethanol and the best way to stabilize the gas for your push lawn mower here.
Bad Fuel Pump
Most push mowers do not use a fuel pump. Yours will use one if the carburetor is placed higher on the mower than the fuel tank. A fuel pump will be needed to work against gravity to move fuel upward to the carburetor.
Your vacuum fuel pump can wear over time because the makeup of fuel today can degrade plastics causing leaking at the plastic seams. When the plastic is compromised, your fuel pump is no longer able to build the pressure it requires to pump fuel to the carburetor.
Depending on your push mower, you will either have a high-density polyethylene tank or a metal fuel tank. The seams can fail on the polyethylene tank resulting in a fuel leak. If you find a leak, it is best to replace the fuel tank.
Fuel sitting in a metal fuel tank can cause it to corrode and leave rust spots that may eventually develop a hole. In this case, I prefer to replace the fuel tank so I don’t have to worry about additional rusting and contamination of the fuel system.
However, if the tank is on an older mower and is no longer being manufactured, you may not have this option. You can attempt to repair the rusted spot.
Faulty Shut-Off Valve
Some push mowers will have a fuel shut-off valve located at the bottom of the tank. This valve does exactly what its name suggests.
It shuts off and turns on the fuel supply to the mower. Fuel shut-off valves are prone to leak and must be replaced once you find gas coming out of the valve.
Fuel lines will become dry and brittle with age. They will develop cracks over time where fuel will begin leaking.
Any cracked fuel lines need to be replaced. You will also need to look for tears or punctures in the fuel line where the hose clamps attach.
Bad Gas Cap Seal
The gas cap has a rubber gasket so it securely seals to the fuel tank. The gasket can become dry and fail. It will allow fuel to seep out of the tank around the fuel cap.
Because gas evaporates, you may only smell gas in the air and not have noticed the wet spot from outside of the fuel tank.
To determine if your gas cap is leaking, rock your mower back and forth to slosh fuel up to the fuel cap. Watch for a wet spot to form outside of the tank around the cap. Replace the fuel cap if you see it leaking.
Still Having Problems with Your Push Mower?
Push mower owners encounter many common problems over a mower’s lifespan. Every mower develops issues over its lifespan even when purchasing a top-of-the-line lawn mower.
To help you identify the causes of these problems and how to fix them, I put together this guide to help: Common Push Mower Problems & Solutions.