Reasons Why Your Cub Cadet is Leaking Gas

Your Cub Cadet mower storage area smells of gas, but you can’t find any signs of a gas leak. It can be tough to find a gas leak if it is not a significant amount of gas. Gas tends to evaporate therefore making it pretty hard to spot a leak.

Cub Cadet lawn mowers can begin leaking gas from the carburetor, fuel cap, fuel lines, fuel filter, fuel pump, fuel tank, fuel shut-off valve, and primer bulb.

A fuel leak is a pretty common problem to have as a lawn mower owner. I will share the most common places to check for a fuel leak on your Cub Cadet.

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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.

Reasons Your Cub Cadet is Leaking Gas

Cub Cadet Carburetor

The carburetor has many parts that can get clogged or fail. This is why there is a highly likely chance your gas leak is coming from the carburetor because this is the place where a small amount of fuel is stored after it leaves the fuel tank.

Carburetor Bowl

Check the bottom of the carburetor. This area is called the carburetor bowl. There is a very thin o-ring between the base of the carburetor and the bowl that can become dry and fail to seal correctly. This o-ring looks much like a rubber band.

This is a very common place for your carburetor to leak because the o-ring is subjected to the heat of the engine. The area consistently goes from hot to cold temperatures putting stress on the o-ring causing it to become hard and lose its ability to seal.

Replacing the small rubber gasket at the bottom of the bowl is a very simple process. You will need to get the make, model, and spec number off of the engine and take it to your local Cub Cadet dealer to get the correct o-ring gasket to stop the leaking.

Once you have the replacement gasket, shut the fuel off to your mower using the fuel shut-off valve. If your mower does not have this valve, use clamps to stop fuel flow. Unscrew the screw at the bottom of the carburetor and drop the bowl down.

Replace the gasket and reinstall the bowl and tighten the screw. Turn the fuel back on and wipe down the carburetor bowl. Inspect the carburetor to make sure there are no more leaks.

Stuck Float

Move on to looking at the opening of the carburetor. Your float could be stuck if you find you have a fuel leak coming from the air intake port. This float regulates how much gas can be stored inside the bowl.

If the float gets stuck, it won’t be able to regulate and shut off the gas stored inside the carburetor bowl. Because of this, gas can continue to flow and run out of the carburetor. You can take your carburetor apart to identify and fix the reason why your float is stuck.

If you are not mechanically inclined, I recommend you have your lawn mower repair shop repair the stuck float. If you want to attempt cleaning your own carb, check out my carburetor cleaning instructions here.

Stuck Float Needle

Inspect the carburetor needle. The needle helps get gas flowing to the bowl along with the help of the float. Sometimes the needle will become stuck.

You can try using a soft mallet or the handle end of your hammer and gently hit the side of the carburetor to try to free the needle. This may work a time or two, but it will be a short-term fix. You will eventually need to rebuild your carburetor.

Cub Cadet Fuel Lines

Starting at the fuel tank, follow your fuel lines and check for fuel leaks. If the lines are dry and cracked, they need to be replaced. An area on the fuel lines to take a good look at is the area where the hose is secured with a hose clamp.

Many manufacturers use pinch-style clamps that can damage the hoses more quickly than worm gear-style clamps. You may want to replace the pinch-style clamps with these style clamps found on Amazon or your local hardware store.

Cub Cadet Fuel Tank

Depending on the age of your fuel tank, you may develop a small rust hole on a metal fuel tank. You may experience leaks at the seams of a molded plastic tank.

Over time, the seam on the plastic tank can separate. If either of these reasons is the cause of your fuel leak, you must replace your fuel tank.

Cub Cadet Fuel Valve

Your fuel tank may have a fuel shut-off valve located on the bottom of the fuel tank. The valve allows you to start and stop fuel flow. Some valves are plastic while others are metal. Both styles are prone to leaking.

Cub Cadet Fuel Filter

When gas sits in the plastic inline fuel filters for a period of time because it hasn’t been changed at normal intervals, it will become weak and soft. You will need to check for cracks in the plastic. Replace your filter if it is the culprit to your Cub Cadet leaking gas.

Bad gasoline ran through your Cub Cadet is corrosive and can do damage to your fuel element. Using a recreational fuel without any ethanol content with cause fewer problems to your fuel system. You can read more about the gas to use in your Cub Cadet in this article.

Cub Cadet Fuel Pump

The plastic in your fuel pump can begin to deteriorate due to bad gas much like the effects of fuel on your fuel filter. Most fuel pumps used in lawn mowers are plastic.

Gas that sits in your fuel pump over a number of years begins to rot the pump. The diaphragm and the seams of the pump may begin to leak.

Cub Cadet Gas Cap

When you have checked all of the above items for your fuel leak and still can’t find a leak, the gas cap could be your problem.

You may not be able to see gas leaking from your Cub Cadet because it may be splashing out of the fuel tank and evaporating into the air before you notice a wet area around the tank cap.

If you continually smell gas, but never find the source, check your fuel cap. To identify whether you have a bad cap and seal, shake your mower to slosh the gas up to the cap area and watch to see if you develop a wet spot around the cap.

If you do, you need to replace the cap to prevent your Cub Cadet gas leak.

Cub Cadet Primer Bulb

Some smaller Cub Cadet mowers utilize a primer bulb. This bulb can fill with fuel and begin to leak. It can also become dry and cracked. You will need to replace the primer bulb when it is no longer working efficiently and seeps gas.

In Summary

To find a fuel leak in your Cub Cadet mower, the best thing to do to make sure you check every place a fuel leak can develop is to check the fuel tank, cap, and fuel shut-off valve.

Then continue checking for leaks by following the fuel lines out of the tank and looking at every component fuel runs through including your filer, fuel pump, and carburetor.

The Best Type of Fuel for Cub Cadet Lawn Mowers

The best type of fuel to use in Cub Cadet lawn mowers is a non-ethanol fuel, however, it is okay to use regular gas. Regular gas is unleaded gas with an octane rating of 87 or greater.

This gas must contain no more than 10% ethanol. Read “This is the Type of Gas Cub Cadet Lawn Mowers Use” for more details on selecting the right type of gas.