How to Tune Up a Lawn Mower in 3 Easy Steps

Updated: Apr. 14, 2024

Before you roll it out of the garage in the spring, take some time to tune up your lawn mower to keep it running smoothly and effectively.

Every small engine needs regular maintenance to keep it performing at its best. That includes your lawn mower.

When to Tune Up a Lawn Mower

Before you fire it up and cut your first blade of grass this season, we recommend taking the time to tune up your lawn mower, that way it’s ready for spring and will stay running smoothly and efficiently all season.

DIY vs. Professional Lawn Mower Tune Up

The standard tune up is easy to do yourself. There are three main things on your lawn mower that need your attention when you’re tuning it up: the air filter, the spark plug and the oil. Every machine is a little different, whether your have a riding lawn mower or a walk-behind mower, so before you start, check the owner’s manual for the manufacturer’s recommendation on how often to clean or replace each of these things. The manual will also tell you where the parts are located, how to remove them, etc.

If you’re noticing other problems with your lawn mower, like black smoke from the engine or poor performance after a basic tune up, it might be time to take it to a repair shop.

Sharpening Your Lawn Mower Blade

It’s a good idea to sharpen your lawn mower blade in the spring too, and it’s a relatively easy DIY task. However, these instructions are focused on tuning up the engine itself.

Step 1: Change the Lawn Mower’s Air Filter

A clean air filter helps maintain the proper fuel/air ratio, allowing the mower to burn less gas. Lots of dirt, grass clippings and the debris get into the air filter over the spring and summer, which is good because that’s it’s job! However, as it builds up, it will eventually get dirty enough to throw off the ration of air and fuel going into the engine, causing your mower to smoke, sputter or even prevent it from starting.

Once you locate the filter, remove the cover and pull out the old air filter and pop in a new one. In some cases you can get away with cleaning it, but it’s best to start the season with a new one.

On some machines, there may be a foam filter between the casing and the air filter itself. That catches the larger debris. Remove the foam filter and wash it in the sink.

Step 2: Check the Spark Plug

The spark plug is one of the most important elements in your lawn mower’s engine. It’s what ignites the fuel and air mixture inside the cylinder and makes the engine run. It’s usually easy to see where the spark plug is on a walk-behind mower, but you’ll probably have to lift the engine cover to access it on a riding mower. Don’t forget to check the lawn mower fuel filter.

The spark plug itself is covered by a thick rubber cable that you’ll need to remove to check it. Using the correct size socket, remove the spark plug. If the plug’s rusted tight, spray it with a penetrating lubricant and let it soak in for 10 minutes before trying to loosen the plug again.

If the old spark plug has a carbon (the black, sooty stuff) built up on it, that means that it’s time to replace the spark plug. You can clean it off with carburetor cleaner and a wire brush, but it’s generally better to replace it. (A new plug costs around $6.) Make sure you’re replacing it with the correct spark plug, the one that’s recommended by the manufacturer.

You used to have to check the spark plug gap, i.e. the space between the electrode and overhanging arm, but most new spark plugs come pre-gapped to fit your mower. Still, it’s a good idea to make sure there is a gap there in case the spark plug has been dropped. If the overhanging arm is bent tight to the electrode, the mower won’t start.

To install the new plug, hand-turn the new plug until the threads catch. Ratchet the plug down until it stops, then turn it another quarter turn (cranking down too hard can break the plug or render it nearly impossible to remove).

Step 3: Change the Oil in Your Lawn Mower

This is an important step. Over time, contaminants and moisture gets into the old oil, which can corrode the inside of your engine.

Before changing the lawn mower oil, remove the spark plug cord. This is a safety measure that will prevent the mower from starting when you tip it up to drain the oil.

Next, pop out the dipstick and tip the mower over until the oil starts draining out. Make sure to drain the oil into a pan, so that you can dispose of it properly and safely. Most counties or cities offer a place where you can take the old oil to be recycled, which helps prevent it from contaminating the ground water.

After the old oil is out, you can add new oil. Make sure it’s the right type of oil for your lawn mower; just check the manual for the manufacturer’s recommendation. Add the new oil with a funnel, to prevent a mess that’s going to be hard to clean up. Let it settle for a few minutes, and then check the dipstick to ensure that the oil is at the proper level.

And with that, you’re ready to cut the grass!