Lawn Mower Not Starting? Try These Fixes


There are parts of the year that you escape mowing your lawn, but as soon as summer starts up again and it gets warmer, you have to get your mower out and start using it. Once you’re ready to make your lawn look really nice and back to normal, then you might run into a bit of an issue.

Sometimes when you haven’t used your lawn mower up for a while, it doesn’t turn out the way you expect it. When this happens, you’ll have to troubleshoot your lawn mower so that you can figure out how to fix it. If you want to get your lawn looking nice again, then here’s how you can troubleshoot your lawn mower to get it back to normal.

How Does Lawn Mower Work

Before you troubleshoot your lawn mower, you’ll need to know how it works. A lawn mower engine is very simple compared to the other motors that you might deal with on a daily basis. Even though it’s simpler, they do operate similarly. These engines are single cylinder and 4 cycle, which means there are four distinct phases or cycles that these engines go through. These engines run on gas also.

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The four cycles of these engines are very important. The first one is the intake, which is when the intake valve opens and mixture is sucked into a hollow cylinder. Then, the second cycle is when the intake valve closes and the mixture that it sucked in is compressed. The third cycle is when the mixture that was compressed is ignited by a spark and it’s burned to generate power after it’s ignited. This increase in temperature and pressure forces the piston to go down the cylinder. This rotates a crankshaft and turns the blade in your mower. The fourth cycle is when the exhaust valve opens and all of the gases are let out of the cylinder.

This is repeated about 20 times per second when your lawn mower is running. If this isn’t repeated, then your lawn mower will stop working. The sharpened blade will spin around at about 3,000 rounds per minute and this cuts your grass as you run up and down your lawn. Because of these cycles, you can kind of detect what issues you might need to inspect to find out why your lawn mower isn’t starting.

Before Repairs

Before you begin working, you’ll want to make sure that you’re safe.

First it’s very important to make sure that all sources of ignition are removed from the area. Gas is very flammable so things with flames, stoves, sparks, cigarettes, or hot objects in general that are in the vicinity can be dangerous. Make sure that all of these aren’t anywhere near your mower so that you don’t start a fire. Also, you should make sure that you have proper ventilation so that you don’t have any buildup of vapor in the area. Commonly people have rags moistened with gas lying around so you’ll want to remove these from the area also.

Remove the spark plug. If you’re going to be working on the underside of the engine, you’ll have to make sure all the controls are off and that the spark lead is disconnected. You also have to make sure the engine is cooled down. If you’re going to start turning the blade, make sure the plug is removed from the engine for safety. It’s possible that even if the plug is disconnected and the cylinder in a hot engine has gas in it, then the vapor could explode when compressed. The engine isn’t on and it won’t run, but it might take the blade to start. It’s unsafe for you so you need to prevent this from happening.

You also want to keep the carburetor side of the engine upwards. This helps you avoid any oil spills, which would occur if the mower was on its side. Engine oil can have difficulty starting up the mower if the oil clogs up the carburetor and the air filter. The reservoir at the bottom of the engine that holds the oil is vented, which is necessary so the air can enter and leave it as the piston moves in and out of the cylinder. This prevents drops of oil from getting blown out of the vent. Some unburned gases may get by this and into the crankcase, which would cause the pressure to rise. The vents prevent all of this from happening. This is why you want to make sure the engine is upwards so that none of this happens.

If the fuel levels are higher than the vent, then the oil might spill. You want to make sure that you drain the gas tank if the motor is on its side. You can collect the gas in a container so that you can use it later. You can also use a siphon pump that’s designed to take all of the gas out of the gas tank. If there’s only a small amount though you don’t need to do this.

Now that you’ve done this, you can begin trying to fix your lawn mower.

Fixing Lawn Mower that Won’t Start

Inspect the Spark Plug

There are few steps so you need to take to determine if your lawn mower spark plug is bad.

1. First, you have to disconnect the spark plug wire.

2. Then, you need to remove the spark plug from the machine.

3. Next, inspect the electrode that’s on the spark plug for any signs of damage.

4. You can determine the condition of the spark plug by looking at the condition of the electrode. Pay attention to whether it’s normal, wet, or carbon covered.

If you notice that the spark plug electrode is worn-out or damaged, you’ll need to replace it.

You should note that you can tell that your lawn mower spark plug is bad if the engine is more difficult to start. The engine only starts due to the gas and the spark. Therefore, if you have gas in your gas tank, it could be the spark that’s missing. If you push your lawn mower and it stutters, then it’ll take several pools of the cord to start. If you also see that the engine cuts out while you’re using it, then it also could be the spark.

You’ll see less power and slower acceleration also with a bad spark plug. You may have noticed that these are very small issues in the beginning, but over time they may stop your lawn mower from starting completely.

Also, if you haven’t replaced your spark plug in a while, then this could be why your lawn mower isn’t starting. You need to replace a spark plug in a standard mower about once per season. If you want to wait even longer, you could do it once every two years. They’re very cheap and they usually only cost you a few dollars. It isn’t a big loss, so you should definitely try this fix if you can. Be sure you research what spark plug is needed for your mower because different kinds of models need different plugs.

Check the Gasoline

One of the things that could cause your lawn mower not to start is old gasoline. First, know that you first have to understand what gasoline breakdown does. When gasoline breaks down additives, it can cause the gasoline to be less combustible. Detergents, alcohol-based octane boosters and water build-up can all degrade the gasoline. If degradation occurs, then it won’t be able to spark and start the lawn mower.

Old gasoline can have these additives in it and if you put it in your lawn mower, it won’t start, causing a few problems. The first thing you might notice is that your mower doesn’t run as smoothly as they used to. In some cases, the gasoline is so old and has many additives in it that it won’t even start. If the water that’s condensed in your gas gets in the fuel tank, this could make the situation worse. If there are any other sediment or deposits that are built up from this old gasoline in the carburetor, then you’ll have yourself a mower that won’t start.

To fix this, first you have to remove the residue that may be choking the engine from the old gasoline. Any gasoline that’s in the tank should be removed and you should not use this gas again. You might need to remove the carburetor and clean it depending on what type of motor you have. Also, you might want to check the fuel line to see if it’s clogged due to the old gasoline you were using.

Definitely go buy new gasoline once you check the carburetor and the fuel line. Risking using old gasoline might end up messing up your Mower and you don’t want to have to buy an entirely new lawn mower.

Defective Ignition Switch

The ignition switch is likely the issue if your lawnmower won’t start when you turn the ignition key. You can use a multimeter (View on Amazon) to see whether the electricity travels between the S and B terminals. If you do think the ignition switch is the problem, you can replace it with a manufacturer approved part. The repair isn’t very hard at all and it should take 15 minutes or less.

1. First, you have to disconnect the battery. Make sure your mower is on a level surface and turn the ignition switch off. Make sure you wear gloves. Remove the bolt connecting the negative cable to the battery and cut the cable away so that it’s not touching the battery post.

2. Now, you can lift the hood to access the back of it. Remove the tabs that lock in place and push the switch out. You can disconnect the wire harness attached to the back of the ignition switch and you can wiggle the plug as you pull on it if it’s a little hard to remove.

3. Install the new ignition switch. All you have to do is connect the wire harness to the back of the new ignition switch and push the new ignition switch into the dash.

4. Engage the locking tabs and lower the hood.

5. Now, you can reconnect the negative cable to the negative battery terminal so that you can reconnect the battery. Lower the seat when you’re done.

Once you’ve done all of these things, you can check to see if your lawn mower is running like normal again.

Hopefully, you can get back to making your lawn look nice at the times where it really matters.


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