How to Tune Up Your Lawn Mower in 3 Easy Steps

Also Learn About Tuning Up String Trimmers

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 lawn mower tune-up. Although it is often possible to get by without one, it is recommended that you provide your machine with this bit of TLC each spring. After all, you have a lot of grass mowing ahead of you this summer. The instructions below show you how to do the job, yourself.

A lawn mower tune-up essentially consists of three tasks (although maintaining your machine over the course of the year entails much more than this), each of which I will describe in more detail below:

  • Changing the Oil
  • Changing the Spark Plug
  • Changing / Cleaning the Air Filter

Before performing this task, you need to warm up the engine. Put just enough gas in the gas tank to get your equipment running. Start your engine and let it run until it runs out of gas. Finally, now that you are ready to perform the lawn mower tune-up, you need to take a safety precaution: disconnect the spark plug wire so that the engine can't start accidentally.

Tune-Up Task 1: Steps for Changing the Oil

  1. Make sure you purchase the right type of oil for your replacement oil. When in doubt, ask where you bought the machine. Or, if you are really desperate, check the owner's manual.
  2. Clean off any dirt around the upper part of the oil tank (where you fill your machine with oil). An old toothbrush comes in handy for this task. Unscrew and remove the dipstick, if your oil tank has one.
  3. Now locate the lower side of your oil tank – a plug found on the underside of your machine. You need to drain out the old oil, and unscrewing this plug will do just that. Prop up your machine accordingly with blocks, providing a tilt that will give you access to the plug. Stick an oil pan or like container under the plug to catch the oil. Ready? All right, unscrew the plug (you may need a socket wrench) by turning counter-clockwise and let that dirty oil pour out. And I do mean dirty: obviously, you do not want to have your Sunday best on when performing this job.
  4. Screw the drain plug back on using a clockwise motion. Do not over-tighten, so that you will be able to get it off easily next time you need a tune-up. Rather than over-tightening when you work on your machine, it is better to tighten moderately, then periodically check during the mowing season to ensure that it hasn't loosened through vibrations.
  5. (For machines that have an oil filter) If your machine has an oil filter, replace it as part of the lawn mower tune-up and clean the gasket with which it comes into contact.
  6. Remove the blocks so that your machine is level again.
  7. Fill the oil tank with new oil to the correct level, replacing cap and dipstick.
  8. Refill lawn mower with gas and reconnect spark plug wire.
  9. At this point in the lawn mower tune-up, it's time to start the machine. Let the engine idle and ensure that there are no oil leaks.

Tune-Up Task 2: Steps for Changing the Spark Plug

  1. Disconnect spark plug wire.
  2. Clean the housing around the old spark plug.
  3. Remove the old spark plug with a socket wrench.
  4. Unfortunately, at this point you will have to check the blasted manual again (don't you just hate that?) What you need to do is ensure that the new spark plug is gapped the way it is supposed to be for your machine. Just measure the gap, then see if the measurement matches manufacturer's specifications for your machine. If it does not match (or if there is no gap at all), you will have to create or alter the gap.
  5. Screw on the new spark plug (not too tight!).

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.

Tune-Up Task 3A: Steps for Changing a Paper Air Filter

  1. Unscrew the cover and remove the paper air filter.
  2. Insert a new paper air filter with the pleat facing out.
  3. Screw the cover back on.

Tune-Up Task 3B: Steps for Cleaning a Foam Air Filter

  1. Unscrew the cover.
  2. Remove air filter unit and discard the old foam.
  3. Clean the air filter unit with kerosene.
  4. Soak the new piece of foam in clean engine oil. Squeeze out the excess oil using a clean rag.
  5. Insert new foam in air filter. Ensure the lip protrudes over edge of the unit.
  6. Screw the cover back on.
  7. Re-connect the spark plug wire.

Or perhaps you do not want to be burdened with performing this kind of maintenance (or with paying someone else to do it)? An alternative is to use a battery-powered lawn mower.

There is also the issue of tuning up string trimmers. To learn how, continue reading.

How to Tune Up String Trimmers, Including How to Choose the Right Fuel

The information below comes courtesy of Kris Kiser, President and CEO of the Outdoor Power Equipment Institute.

String trimmers (also known as weed whackers, weed eaters and line trimmers) can help make landscapes neat and tidy by allowing you to edge and trim weeds, grass and overgrowth without having to use handheld shears and trimmers. But before you power up your machine for the first cut of the season, here are some tips on how to get it ready for action.

Gas String Trimmer Tune-Up Tips: Getting Your Machine Ready for Another Year of Work

1. Replace the spark plug and air filter.

With the engine off, remove the old spark plug and air filter. Put in a new spark plug and a fresh air filter to ensure your string trimmer runs more efficiently. 

2. Change the string, if needed.

When the string trimmer requires a new cutting line, you can either wind new line onto the existing reel or install a new spool. For either option, first remove the spool by taking off the cap. Then, clean the surface of the outer spool, inner spool and drive shaft with a clean rag.

If you are replacing the spool, insert the new spool now. To rewind an existing spool with new string, measure about 50 feet of new line and insert each end of the line into the holes on the inner spool. Following the direction arrows indicated on the spool, wind the line tightly onto the reel following an even pattern.

When you are finished, insert the ends of the line into the notches. Now, you'll need to reinstall the spool by inserting the ends of the line into the holes in the outer spool and pulling the line through the holes. Reattach the cap. 

3. Use the right string trimmer line.

It is important to note that different string trimmers require different types and sizes of line, so you must be careful to select the right line for your product. Using the wrong string can cause the line to break. If the line breaks, it may be launched at you, or at another person or object. Your operator's manual should indicate the type of line you need. If all else fails you can remove the spool and/or line and take it with you to ensure you purchase the right kind.

4. Choosing the right fuel: the problem with higher ethanol fuel blends.

Gas powered string trimmers are handy because they give you freedom to maneuver without a power cord. But using the wrong fuel in your string trimmer can damage or destroy the machine. Some gas stations now offer higher ethanol fuel blends, such as E15, E30 and E85. But using fuel blends above E10 in string trimmers, lawnmowers, leaf blowers and other small engine equipment will damage or destroy the products. Look before you pump, and select the right fuel for your string trimmer and other small engine equipment.

How to Use String Trimmers Safely

OK, you've tuned up your string trimmer now. You've cleaned it and changed the spark plug and air filter. You've put on a new line (if necessary) and ensured that you're using the right gas for it. You are ready to turn it on and tackle your next project. But not so fast. First, it's important to take a few steps to ensure you and the people, pets and property around you, stay safe. So here are some string trimmer safety precautions to remember:

1. Read the owner's manual.

Familiarize yourself with the operating instructions and safety measures for your particular unit. 

2. Dress properly.

Wear eye and ear protection, gloves, closed-toe shoes, and snug-fitting long-sleeved shirts and long pants.

3. Clear your work area.

Remove sticks, rocks, wires and other foreign objects that could be flung at you or others as you trim. Make sure there are no people or pets within 50 feet of the area in which you'll be working.

4. Stand strong.

Grip both of the machine's handles firmly, with each hand wrapping fully around the handles. Avoid uneven, sloped and slippery surfaces. Never work on a ladder and don't overreach.

5. Cut in the right direction.

Always cut away from yourself to keep dirt and debris from being propelled out of the string trimmer head toward you. For more maintenance and safety tips for all types of small engine equipment visit

Editor's note: Want the freedom of going cordless without having to worry about unintentionally filling up with a higher ethanol fuel blend? Propane could be the answer. Read this review of a propane string trimmer. For more on staying safe in your landscaping endeavors, see these yard safety tips.

Disclaimer: If you have any doubts regarding your ability to perform the tasks above without causing harm to body or property, have your unit serviced by a professional.