Get Your Lawn Mower Winter Ready
Step 1: Empty the gas tank
Unused gas left in a mower over the winter can get stale, gumming up the carburetor and inviting rust. First, add fuel stabilizer to the tank, then run the mower to distribute it through the system. Turn the mower off and allow the engine to cool, then siphon excess gas into a clean can. (You can put this gas in your car, provided it hasn’t been mixed with oil.) Restart the mower and run it until it stops; repeat until the engine no longer starts and the fuel lines are empty.
Before continuing with the remaining maintenance steps, it’s very important that you disconnect the spark plug to prevent the mower from kick-starting accidentally, which could lead to serious injury.
Step 3: Remove the blade
To make it easier to change the oil and clean the underside of the mower, first detach the blade by unscrewing the bolts that hold it in place. Be sure to wear thick gloves when handling the blade. While the blade is off, take advantage of the opportunity to sharpen it
Step 4: Drain the oil
If the mower has a 4-cycle engine, you’ll need to change the oil. (Some mowers and most trimmers have 2-cycle engines, in which the oil is mixed with the gas.) Have a pan ready, and place a tarp under the mower to catch any oil that might spatter. Set the mower on its side with the air filter and carburetor facing up, so oil and residual gas don’t spill into them. Remove the oil reservoir plug and slowly tilt the mower until the oil begins to drain into the pan. Replace the plug when all the oil has drained.
Use a putty knife and wire brush to scrape off the grass and mud caked on the mower deck. This prevents rust, clears the passageway to the discharge chute, and allows the aerodynamics of the deck to work as designed. With the deck cleaned, reattach the sharpened blade. Once you’ve finished and can turn the mower upright, fill the oil tank with fresh SAE 30 or 30-weight oil, and recycle the used oil at a service station. Don’t use a thicker oil, such as 10W-40.
Step 6: Change the air filter
A dirty air filter keeps the engine from burning gas efficiently by restricting the air needed for combustion. If your mower has a paper filter, replace it with a new one, paper edges facing out. If it’s an oil-soaked sponge filter, remove it, wash it out with soap and water, allow it to dry completely, and then add a bit of clean oil to it before putting it back. Clear the cooling fins of dirt and debris using a screwdriver or popsicle stick.
Step 7: Replace the spark plug
Remove and replace the spark plug, using a socket wrench with a spark-plug socket, which has a neoprene lining to protect the plug’s porcelain casing. Even if the old spark plug is in good shape, for a couple of dollars a new one will perform better and ensure a smooth start come spring.
Source: This old House