You smell gas coming from the mower, but you’re not sure exactly where it’s coming from. Sometimes it’s easy to find a fuel leak, but it can become increasingly harder once the fuel has evaporated leaving no wet spot behind.
A Simplicity lawn mower may begin leaking gas from the carburetor, fuel filter, fuel shut-off valve, fuel line, fuel pump, gas cap, or a bad fuel tank.
Gas fumes are harmful. Always work in a well-ventilated area away from combustible items. Wait for the engine to cool and remove the spark plug boot(s) before making repairs.
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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 Simplicity Lawn Mower May Be Leaking Gas
Carburetor is Leaking Gas
It is common to develop a fuel leak at the carburetor. This is the place where a little gas is stored after it leaves the fuel tank.
This old gas leaves behind a varnish that can cause the internal parts to stick and not function correctly. This may result in a leak.
When you find the carburetor is leaking, check the carburetor gasket, stuck float, and stuck float needle.
Carburetor Bowl Gasket Failure
The first place to check when you find the carburetor is leaking is at the gasket that sits between the carburetor and the bowl at the bottom of the carburetor. This is the bowl where fuel is stored.
This gasket looks like a rubber band. It can become dry and brittle over time. This is mostly because of its proximity to the engine.
Being close to the engine, the gasket is subjected to swings in temperature that put stress on the gasket. The gasket gets hot when the engine is running and cools down when it is not.
Due to the extreme temperature changes, the gasket can become dry losing the ability to seal the bowl to the carburetor. Fuel will begin to leak out of the bowl.
If you do find a leak between the carburetor and the bowl, you will have to replace the carburetor gasket. Obtain a replacement gasket for your model engine carburetor.
You will need to get the model and spec number from the engine to get the correct gasket. Note: This is different from the mower model and serial number.
Follow these steps to replace the carburetor gasket on a mower:
- Wipe around the outside of the carburetor to remove dirt and any debris stuck to it.
- Remove the screw located at the bottom of the carburetor bowl. Have a rag ready to collect any gas remaining in the bowl.
- Lower the bowl to remove it.
- Remove the old gasket and replace it with a new gasket.
- Don’t get any lubricants on the new gasket so you don’t damage it.
- Reinstall the bowl and secure it by tightening the screw.
If you didn’t find a leak coming from the gasket or you repaired the gasket leak and continue to have a leak coming from a different area of the carburetor, look near the top of the carburetor by the air intake port.
When gas is leaking from this area, the most likely issue is a stuck carburetor float. The float is the part that regulates the amount of fuel that is allowed into the bowl.
So, when it becomes stuck, the float may not be able to stop gas from flowing into the carburetor bowl. It can cause your Simplicity mower’s carburetor to overflow and run out of the carburetor.
A leak that is caused by a stuck float must be repaired by disassembling the carburetor and repairing the stuck float. You may be able to clean your carburetor to free up the float.
You may end up having to rebuild the carburetor using a rebuild kit or replacing the carburetor depending on the condition of the carburetor.
Stuck Float Needle
Once you get inside your carburetor to look at the float, you may find the float is fine and the float needle is actually stuck. The needle works with the float to keep gas flowing into the bowl. When the needle is stuck, you must rebuild your carburetor.
To temporarily loosen your stuck needle, tap the carburetor with a rubber mallet. A rubber handle on a tool also works well.
This may work once or twice, but eventually, you will have to replace the float needle to correctly fix your carburetor.
Check the fuel filter. It could be damaged or the plastic can become weak and begin to leak.
When the filter isn’t regularly replaced, gas can begin to degrade the plastic housing and it can begin leaking at the seams.
You must replace a leaking Simplicity fuel filter. Be careful replacing a plastic inline fuel filter. The ends of the filter can become soft and may break off in the fuel line if you are not careful.
To help prevent the filter from leaking at the seams in the future, replace it annually. The fuel filter is essential to keep dirt out of the fuel system so it doesn’t cause engine wear.
A plastic fuel pump can begin leaking for the same reasons as the fuel filter. Check the seams of your fuel pump for leaks. Replace the fuel pump with a new one when you find a leak.
Fuel Tank Seam
The fuel tanks used on a Simplicity lawn mower are made of high-density polyethylene material. These tanks may fail at the seams and begin leaking.
Replace the fuel tank when you find it is leaking at the seams.
Fuel Shut-Off Valve
A lawn mower has a fuel shut-off valve located near the bottom of the fuel tank or inserted between the fuel line. Fuel valves are prone to leaking and must be replaced when this happens.
As the fuel lines age, they will become dry. Fuel may begin leaking from the cracks.
Follow the fuel line coming out of the fuel tanks. Check the fuel lines, hose connectors, and clamps to ensure there are not any loose connections or tears from the claps that can cause a leak.
Replace a fuel line where you find a leak. Pay attention to the diameter of the fuel line so you purchase the correct replacement hose. It is also good practice to replace the lines that dry and develop cracks before they begin to leak.
When replacing your fuel lines, take a look at the clamps. If your mower has pinch-style clamps, I recommend replacing them with worm gear clamps because they are less likely to puncture the fuel line and cause leaking.
Gas Cap Seal
If you’ve gotten this far and can’t find the leak on your Simplicity, it’s time to check the gas cap. Look around the gas cap area for a wet spot.
If you see one, you most likely have a bad seal in the gas cap that has become dry and is no longer creating a good seal. Just because you don’t see a wet spot doesn’t mean you don’t have a bad seal.
Gas evaporates and doesn’t leave a sign of a wet spot if you don’t locate the leak right away. To determine whether the seal is bad and fuel is leaking when gas sloshes around the fuel tank, carefully rock the mower back and forth.
This is to splash fuel up around the tank cap. Don’t get too aggressive. You don’t want to lose your balance or tip the mower.
If you notice a wet area forming around the fuel cap outside of the tank, replace your cap with a new gas cap.