How to Drain and Replace Gasoline In Your Mower

SC 100 Walk-Behind MowersIs your Cub Cadet mower not running right? Are you worried about problems with hard starting and poor idle? In most cases, these problems can be traced to poor fuel. Here’s what you need to know about when, how and why to drain your mower’s fuel system.

Why Do I Need to Drain the Fuel from My Mower?

Gasoline formulations are developed with modern cars in mind, which causes problems with small engines, especially as the fuel ages. How this happens depends on the fuel blend.

Ethanol is hygroscopic, as it sits, it absorbs water and falls out of suspension, which can lead to starting problems and corrosion.

“Pure” gasoline doesn’t benefit from the solvent properties of ethanol, so it degrades quickly. As it breaks down, it varnishes components and forms waxes that clog the fuel line and carburetor.

While the gas you put in the tank of your car will be burned in a week or two, it can take weeks or months to use up the fuel in the gas can you use for your mower. Carburetors also aren’t as good at getting fuel to vaporize, and as that fuel gets older, it doesn’t vaporize as easily. Even without the problems of corrosion and lacquering, the engine will get harder to start as the fuel sits.

When Do I Need to Drain the Fuel?

On most engines, all gasoline needs to be used before it goes stale. Cub Cadet and their engine partners, including Kohler, Honda, Kawasaki and Briggs & Stratton, recommend using fuel within 30 days of purchase. This can be extended to 90 days if the fuel is mixed with a stabilizer shortly after purchase. As a general rule, the fuel system should always be drained before putting the mower into storage for the winter.

There is one exception to this rule: Cub Cadet EFI engines. These can use untreated fuel that is several months old, and they can be stored during the off-season with stabilized fuel in the tank. This is not recommended for EFI-equipped engines from other manufacturers.

Draining Fuel from a Honda GXV630

This engine is used in some versions of the RZT Series ZTR mower.

1. Disconnect the fuel line from the carburetor and place the end of the line in a suitable gasoline container.
2. Once fuel stops draining from the line, reattach it to the carburetor. Loosen the carburetor drain screw, located on the top left side of the air filter cover. Drain this fuel into the gas container.
3. Tighten the carburetor drain screw.

Draining the Fuel Tank on All Other Mowers

To drain the tank, you will need a siphon pump. If you have a walk-behind mower, do not try to tilt the mower to let fuel pour out of the gas tank: this will flood the carburetor and possibly soak the air filter.

Fuel should be drained only when the engine is cold. Disconnect the spark plug or plugs to prevent the engine from starting accidentally.

1. Unscrew the gas cap.
2. Place the suction tube of your siphon pump in the tank, and the outlet tube in a gas container.
3. Prime the pump by moving the handle up and down or squeezing the priming bulb two or three times. Once fuel starts flowing, it will continue without needing to be hand-pumped.

Draining the Fuel Lines and Carburetor

Once the fuel tank is empty, the rest of the fuel can be drained by starting the engine and letting it run until it stalls. This should be done on all carburetor-equipped engines, including the Honda GXV630, before storing to remove remaining fuel inside the float bowl and jets.

What Can I Do with Stale Fuel?

If the fuel is clean, the EPA recommends adding it to the tank on your car or truck. Fuel-injected engines are less sensitive to stale fuel, and this fuel will be diluted by the gas already in the tank.

If the fuel is contaminated with debris or water, it should be taken to a hazardous waste center for disposal.

Need to Fix Your Cub Cadet?

If it’s Cub Cadet, you can get it from We offer a full selection of OEM parts for Cub Cadets and their engines including hoses and carburetor parts, as well as StarTron fuel stabilizer. Our site can find parts based on your model and serial number, and factory diagrams are built into the search so you can be sure you’re ordering exactly what you need. We ship across the U.S. and Canada.

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