Why Your Riding Mower is Leaking Gas (Fixed!)

You may notice your riding mower is leaking gas when you see a wet spot on the ground or signs of burnt grass in your yard. Most times, you don’t even notice you have a gas leak until you smell it in your garage or storage area.

It can be difficult to find the point where your mower’s leak is coming from especially once the gas has evaporated.

A riding mower may begin leaking gas due to a stuck float or bad gasket in your carburetor; a cracked or degraded fuel pump, fuel filter, fuel line, or fuel tank; or a bad seal in your gas cap causing fuel to seep out of the cap when operating your mower.

You will find a complete list of items to inspect when looking for the cause of your fuel leak.

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Follow all safety instructions provided in your equipment operator’s manual prior to 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.

This is Where Your Riding Lawn Mower Is Leaking Gas

Carburetor is Leaking Gas on Your Riding Mower

A carburetor can be the source of the fuel leak on your riding mower. This is where a small supply of gas is stored after it leaves the fuel tank. Gas that sits in your mower can leave gummy and crusty deposits in your carburetor causing the parts in your carburetor to fail.

Failing parts can cause your carburetor to start leaking. The most common items in your carburetor that can contribute to a leak are a gasket failure, a stuck float, or a stuck float needle.

Gasket failure in the carburetor bowl

Check the gasket around the carburetor bowl. The bowl is located on the bottom of the carburetor. The gasket that sits between the bowl and the carburetor can become dry and brittle due to its location on your riding mower.

Because it is placed right next to your engine, it is exposed to heating while your mower is running and cooling when it’s not. This constant change in temperature puts stress on the gasket causing it to lose its sealing capabilities.

If you identify a leak from the carburetor bowl, you must replace the gasket. This gasket, which looks like a rubber band, is easily replaced. First, you need to buy a replacement gasket.

To find the right gasket, get the model and spec number off your engine. You can bring this information to your local engine dealer or use it to look up the correct gasket to buy online.

Next, with the new gasket in hand, begin replacing your gasket by following these steps:

• Shut off the fuel supply. Use the fuel shut-off valve under your fuel tank.
• Have a rag available to catch the fuel remaining in your bowl.
• Remove the screw at the bottom of your carburetor bowl and remove the bowl.
• Remove the old gasket and replace it with the new gasket.
• Reinstall the bowl and tighten the screw at the bottom of the bowl to secure the bowl to the carburetor.

Stuck float in your riding mower carburetor

If your carburetor is continuing to leak, move on to checking for a stuck float. Check to see if your leak is coming from the area near your air intake port. A stuck float can cause fuel to leak in this area.

The float’s purpose is to regulate the amount of fuel allowed into the carburetor bowl.

When a float gets stuck, it is no longer able to regulate fuel. The fuel will continue to flow into the bowl and begin to overflow. If the stuck float is the cause of your fuel leak, you will have to take your carburetor apart to determine why your float is sticking.

You may be able to clean your carburetor to “unstick” the float or you may have to rebuild it. You can find steps to clean your carburetor here.

Stuck float needle in your riding mower carburetor

You may find the float is okay, but the float needle is stuck. The needle works with the float to keep gas flowing into the carburetor bowl.

When the needle is stuck, your carburetor needs to be taken apart and rebuilt. You can do this yourself or have your local lawn mower repair shop fix your carburetor.

A stuck needle may be temporarily fixed by tapping the carburetor with a rubber mallet or the rubber end of a hammer. This solution may work for a time or two, but eventually, you will have to replace your needle.

Riding Mower Fuel Filter is Cracked or Deteriorating

The gas that sits in your riding mower fuel filter can degrade the plastic housing making it soft and weak. Your fuel filter can begin to leak at the seam when this happens.

It can also leak if your filter becomes damaged and cracked. Replace your fuel filter if it is the culprit of your gas leak.

Be careful when replacing your fuel filter. The plastic can be soft and the ends of the filter can break off inside your fuel hose. You can find a replacement fuel filter online or at your local hardware store.

To find out more information about the negative effects gasoline can have on your riding mower, check out my article on lawn mower gas.

Bad Riding Mower Fuel Pump

Gas not only degrades and negatively affects fuel filters, but it can also damage the fuel pump. Check the seams of your fuel pump for leaks.

A fuel pump with a fuel leak must be replaced. You can purchase one at your riding mower retail store or online. An aftermarket fuel pump I’ve had good success using and have sold to my customer over many years is this one.

Riding Mower Fuel Tank

Your fuel tank may be metal or made with a high-density polyethylene material depending on the age of your riding mower. A metal tank can develop rust holes and begin to leak.

Many of these older metal tanks are no longer being made so it’s hard to find a replacement. Your only option may be to patch the hole in the tank.

Newer riding mowers use polyethylene material that can become weak at the seams and leak. In this case, it is best to replace the tank with a new tank.

Riding Mower Fuel Shut-Off Valve

The next place to look for a fuel leak is the fuel shut-off valve on the bottom of your gas tank. Shut-off valves are known to leak whether they are made of metal or plastic. Replace the valve if you find it leaking.

Old Fuel Lines on Your Riding Mower

Fuel lines can become dry and brittle with age. They can develop cracks causing gas to leak from your riding mower.

Another place that is known to leak on your fuel lines is in the areas where clamps are used to secure your fuel lines. The clamps can either be loose or puncture the hose.

Any cracked fuel lines need to be replaced. This may also be a good time to replace the fuel clamps if your mower uses a pinch-style clamp. I like using a worm gear clamp because they are less likely to pinch your lines and cause leaking.

Bad Riding Mower Gas Cap

There is a seal in your riding mower’s gas cap. This seal can go bad and fail to seal your tank properly resulting in gas leaking around the cap. Gas evaporates in the air so you may not notice a wet spot around the gas tank cap.

To check to for a fuel leak in this area, rock your mower back and forth to splash fuel up around the cap area. Replace your gas cap with a new cap if you notice a wet spot developing around the outside of your cap.