How to Repair a Lawn Mower

Remove the spark plug before you start any repairs.

It’ll make sure the blade doesn’t start up. Find the spark plug, grab the cap, and pull it straight off. Then, use a spark plug wrench to unscrew and remove the spark plug so you can inspect it and safely repair the mower. If you don’t have a spark plug wrench, you can use a socket wrench instead.

Replace the air filter if it’s dirty.

A dirty filter can cause your mower to break down. Find the air filter on the side of your mower’s engine. They’re usually covered by a plastic or metal cover. Use either a screwdriver or a wrench to remove the screws or bolts and take off the cover. Pull out the filter and inspect it for cracks, tears, or holes. If the filter is really dirty, swap it out for a new one that’s the same make and model. If your mower’s engine is running really rough, loses power while you’re using it, or won’t start up at all, it could be because the filter is clogged or damaged.

Pull out the dipstick to check the oil level.

Add more oil if your mower needs it. Look for a handle near the top or on the side of your mower’s engine. Pull the handle to slide out the dip stick. Wipe the stick on a clean cloth, reinsert it into the mower, then slide it out again to check the oil level. If it’s low (there’s usually a line on the dipstick that indicates how much there should be), top it off with the oil specified in your owner’s manual. Replace the dipstick when you’re finished. Having too little oil can cause your mower’s engine to overheat and shut down. Make sure you use the oil your owner’s manual says to use. Otherwise, it could damage your mower’s engine. If you don’t have your mower’s owner’s manual, try looking up the make and model online to see what oil to use.

Drain and replace the oil if it’s black.

Dirt can damage and affect your mower’s performance. Lawn mower oil should be golden brown and there shouldn’t be any dirt or debris floating in it. If your oil is dirty or dark, tip the mower over on it’s side and allow the oil to drain completely into a container. Then, fill it back up with the oil specified in your owner’s manual. Go online to find a used oil collection site so you can properly dispose of your old oil.

Replace the fuel in your mower if it’s old.

If it was left in the tank over the winter, it can affect your engine. Use a siphon to safely remove the fuel from the tank of your mower into a fuel-safe container. Once the tank is completely empty, refill it and try starting it up. Check your local guidelines about how to properly dispose of old fuel.

Tighten your spark plug if it’s loose.

Use a wrench and turn it clockwise. Look for the spark plug on the side of your mower’s engine. It’ll look like a small piece of metal pointing sideways and covered by a protective rubber cap. Over time, the plug can get loose in it’s socket. Fortunately, it’s a pretty easy fix. Take a wrench and give it a gentle turn until it’s tightened up. If you were having trouble starting your mower, give it a go and see if that helps. If tightening the spark plug doesn’t work, you’ll need to remove it before trying any other repairs.

Look for a loose or disconnected wire around the spark plug.

Remove the spark plug cap to inspect the wiring. Check to see if the wire that connects it to your mower is loose or disconnected. If it is, firmly push the wire back into the spark plug. If your mower wasn’t starting, try reinstalling the spark plug by screwing it back into place and starting it up to see if that fixes the issue.

Clean the spark plug if it’s dirty.

Use a wire brush and some spark plug cleaner. Take a rag and clean the area around the spark plug on your mower to help keep dirt and gunk from getting onto the plug. Apply spark plug cleaner to the plug and use a wire brush to gently brush any deposits. It’s pretty common for oil, grease, grime, dirt, and grass to get onto your spark plug, which can prevent it from working properly. You could then reinstall the plug by screwing it back into the socket and test out your mower if you were having issues starting the engine. Look for spark plug cleaner at your local auto repair shop.

Check the spark plug for corrosion and cracks.

Replace it with a new one if it’s defective. Look all over the spark plug to see if you can find rust, chips, or cracks anywhere on the surface. If you do, swap out the plug for a new one of the same make and model so it’ll work in your mower. You can find spark plugs at your local auto repair shop. They cost about $10-$15 USD. Pro tip: bring your old spark plug with you so you can make sure you pick out the right replacement.

Clean or replace the fuel line if it’s clogged.

Blast the line with compressed air or replace it if it’s cracked. Look for a small air hole on the top of your fuel cap. If it’s clogged, hit it with a shot of compressed air to clear it. If the air hole is clear, the problem may lie in the fuel line. Remove the metal housing covering your engine, and lift out the fuel tank. Disconnect the fuel line with a pair of pliers, blast some compressed air through it to clear it, then reinstall it. If the line is cracked or damaged, replace it with a new one. Then, reinstall the outer housing. A clogged or damaged fuel line can cause your mower to not start. If your mower has a valve at the bottom of the fuel tank, switch it to the “Off” position before you remove the tank.

Wipe the underside of the mower if it's dirty.

Grassy buildup can affect the blade and lead to rust. Carefully lift or tip your mower on it’s side over so you can access the blade area. Take a damp cloth and remove any grass build-up that could be affecting the blade. It’ll also help protect your mower against rust. It might seem like a simple fix, but it can be super effective.