How to Tune Up a Lawn Mower in 3 Easy Steps

Hand placing an air filter into a lawn mower.
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Are you tired of yanking on that starter cord until your arm hurts? If your mower is not starting up as soon as it should, perhaps it is time for a lawnmower tune-up. Modern lawnmowers can often run fine without a tuneup at all, but providing this bit of TLC each spring will ensure good, dependable operation for many years.

While there are other routine maintenance tasks involved in owning a lawnmower, the annual tune-up routine consists of just three tasks:

  • Changing the oil
  • Changing the spark plug
  • Changing/cleaning the air filter

Before performing a tuneup, it's best if the engine is just slightly warm. Put just enough gas in the gas tank to get the mower running, then start the engine and let it run out of gas. As a final safety precaution, disconnect the spark plug wire so that the engine can't start accidentally.

Tools and Supplies You Will Need

  • Motor oil
  • Old toothbrush
  • Wrenches
  • Rags
  • Motor oil
  • Oil pan
  • New spark plug
  • Spark plug gapper tool
  • Screwdriver
  • Grease-cutting soap
  • Paper towels

Instructions

Most mowers will operate smoothly for many years with just these three annual tuneup actions. More serious repairs need to be considered only if this tuneup fails to keep your mower running.

How to Change Oil

  1. Purchase Motor Oil

    Make sure you purchase the right type of replacement oil. When in doubt, ask the dealer where you bought the mower, or check the owner's manual. If you no longer have the manual, you can probably find the documentation for your mower online.

  2. Disconnect Spark Plug

    Disconnect the spark plug wire to eliminate any chance of the mower getting accidentally started. To do this, simply slide the collar on the spark plug wire off the tip of the spark plug

  3. Drain the Old Oil

    Clean off any dirt around the upper part of the oil tank—the spot where you fill the machine with oil. An old toothbrush comes in handy for this task. Unscrew and remove the dipstick, if your oil tank has one.

    On the underside of the mower, locate the oil plug. This is usually located on the bottom side of the mower deck, and it may be covered with grass residue if you don't clean the bottom of your mower routinely.

    Prop up your mower right-side-up on blocks, at a slight tilt toward the drain plug. Place an oil pan or other shallow container below the plug, then unscrew the plug counterclockwise and allow all the oil in the crankcase to drain out. You will likely notice how dirty and cloudy this oil is—not like the translucent amber color of new oil.

  4. Fill With New Oil

    Clean off the drain plug with a rag, then screw it back into the drain opening in a clockwise direction. Tighten it securely, but not so tight that you will have trouble getting it off in the future. NOTE: If your machine has an oil filter, also replace this while you are replacing the oil.

    Lift the mower off the blocks, set it on a level surface, then fill the crankcase with new oil to the correct level. Replace the cap and dipstick. Refill the gas tank then reconnect the spark plug wire. Start the mower and make sure there are no oil leaks.

How to Change the Spark Plug

  1. Remove the Old Spark Plug

    Disconnect the spark plug wire. This wire is usually quite evident, with a collar that slips over the top of the exposed tip of the spark plug. Disconnection is a simple matter of sliding the collar off the tip of the spark plug.

    Clean the housing around the spark plug with an old toothbrush and rags. It is important that the area around the spark plug is clean so that debris can't get inside the engine cylinder when you remove the plug.

    Remove the old spark plug with a socket wrench and deep socket (there are special deep sockets designed for removing spark plugs).

  2. Prepare the New Spark Plug

    Consult the owner's manual for information on the proper gap for the spark plug, then adjust the gap between the side electrode and the tip electrode to the proper distance. The easiest way to do this is with a gapper tool. There are several styles for this tool, but they all have some means of easily measuring the gap between the electrodes on a spark plug. The side electrode on the spark plug is fairly easy to bend up or down to adjust the gap.

  3. Install the New Spark Plug

    Screw the new spark plug back into the cylinder on the mower, using the socket wrench. There is no need to overtighten; the plug simply needs to be snug. Reattach the spark plug wire onto the top of the spark plug, the start the mower to check its operation.

How to Change (or Clean) the Air Filter

Before changing/cleaning the air filter, first determine whether your machine has a paper or foam air filter. Paper air filters are replaced, while the foam ones are cleaned.

How to Replace a Paper Filter

  1. Remove the Air Filter

    Disconnect the spark plug wire to eliminate any chance of accidental starting. Unscrew the air filter cover. The cover is usually held in place by a long screw that runs through the filter and is threaded into the bottom of the air filter housing, or it can be secured with a wing nut threaded onto a bolt running through the air filter housing. Removing the screw or nut frees the cover of the air filter, allowing it to be removed.

  2. Install a New Filter

    Remove the old air filter and insert a matching new filter, so the pleats face outward. Reposition the air filter cover, and secure it with the screw or wing nut. Reconnect the spark plug, then start the mower to test its operation.

How to Clean a Foam Air Filter

  1. Remove the Filter

    Disconnect the spark plug wire to eliminate any chance of accidental starting. Unscrew the air filter cover and remove it. The cover is usually held in place by a long screw, or with a wing nut that is threaded onto a bolt running all the way through the air filter housing. Lift out the foam filter.

  2. Wash the Filter

    Wash the foam filter with hot water and a grease-cutting liquid soap. Rinse the filter thoroughly, then press it with paper towels to remove as much water as possible. (Alternately, some users like to rinse the foam in kerosine, but if you do this, it is critical that the foam be allowed to fully dry before reinserting it.

  3. Reinstall the Filter

    Soak the foam filter in clean engine oil. Squeeze out the excess oil using a clean rag. If excess oil remains, it may cause the mower exhaust to emit unpleasant black smoke.

    Check the rubber gasket that seals the air filter to the carburetor. If the gasket has dried out or shows damage, it will need to be replaced.

    Put the filter back in place in the housing, then reattach the cover plate. Reconnect the spark plug wire and start the mower to test its operation.