Why Wont My Lawn Mower Start: A DIY Troubleshooting Guide

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Like any other tool, your lawn mower will have issues after a few uses, such as not starting when you need to use it.

However, not just because you’re having trouble starting your lawn mower, it doesn’t mean you need a new one or bring it to a professional for costly repairs.

Thus, it’s essential to know the answer to the question “Why wont my lawn mower start?” and learn how to check and troubleshoot its common causes.

Why Won’t My Gas Lawn Mower Start?

A gas-operated lawn mower requires more maintenance than electrical models, so issues with the equipment are also more complicated.

Nonetheless, you can easily troubleshoot the common causes of why your gas lawn mower won’t start.

1. Old or Contaminated Fuel

One of the reasons a gas-operated lawn mower has trouble starting is old fuel, especially if you haven’t used the equipment in a long time.

The fuel might be contaminated with excess dirt and moisture.

In this case, all you need to do is drain out the oil in the tank using a siphon pump.

Then, fill it up with new fuel and try re-starting the mower. If it doesn’t start, look at the other possible causes.

2. Filter Issues

The air or fuel filter protects the engine and carburetor from dirt, grass clippings, and other debris. When clogged, it prevents the engine from accessing the gas.

Your lawn mower filter can be either paper or foam.

To check if there’s an issue with the filter, carefully disconnect the fuel line going to the carburetor to check if the gas flows out.

If not, the following can be the cause:

Closed Fuel Shut-Off Valve

This issue is easy to solve as all you’ve to do is open the fuel shut-off valve.

Then, reconnect the fuel line and try starting the equipment.

Dirty or Damaged Filter

If the shut-off valve isn’t the problem or opening it doesn’t solve the issue, here’s what you need to do:

1. Remove the line next to the fuel filter inlet and check if gas flows out freely.
2. If it does, then you just confirmed that the reason your mower isn’t starting is the fuel filter.
3. Remove the filter as per the user’s manual instructions.
4. Replace if you have a paper filter or clean or replace if you have a foam filter.

For the cleaning process, you must:

1. Wash the filter using hot water and mild detergent.
2. Rinse with warm water and allow to dry thoroughly. Wipe the dried filter with fresh motor oil.

3. Spark Plug Issues

If the filter isn’t the issue or cleaning or replacing it doesn’t fix the problem, it’s time to check the spark plug.

It’s the mower’s part responsible for creating a spark to ignite the engine’s fuel.

To check if this is the cause, disconnect the spark plug’s wire and unscrew the spark plug with a wrench.

Inspect for possible problems, such as:

Wet and Dirty

1. Clean the wet spark plug using a carburetor cleaner and allow it to dry.
2. Using compressed air, clean the spark plug and check if there’s oil residue.
3. For any oil residue, spray the plug with a brake cleaner and let it soak for a few minutes and wipe with a clean cloth.

Damaged or Corroded

If you see any corrosion or damages in the spark plug, you must:

1. Purchase a new spark plug, ensuring it’s compatible with your lawn mower.
2. Dispose of any leftover fuel and refill it with a fresh one.
3. Reinstall your spark plug and re-start your equipment. It will usually take a few pulls before you successfully do so.

4. Carburetor Issues

Your lawn mower’s carburetor will help its engine run by ensuring proper air and fuel mixture enters the cylinder, allowing proper combustion.

So, why wont my lawn mower start? It can be due to dirty, clogged, and corroded carburetor.

To resolve this issue, you need to follow these steps:

1. Place a small cup under your lawn mower to catch spills.
2. Loosen the carburetor bowl’s nut using a socket, and then unscrew it manually.
3. Slowly lower the bowl. At this point, the gas should drip out into your catch bowl.
4. Locate the float pin and pull it out, making sure you catch the inlet needle, float, and retaining spin with a clean rag.
5. Carefully remove your mower’s rubber seat using a small pick.
6. Check the carburetor’s internal parts for the presence of powdery or chalky white residues. These indicate that you already need to replace the carburetor.
7. Remove the bowl nut if you don’t need to replace the carburetor.
8. Gently insert a carburetor cleaner straw into the main jet passage.
9. Squeeze the can’s trigger a few times until it shoots into the carburetor’s venturi, indicating an unclogged main jet.
10. If it’s clogged, clean it with the carburetor cleaner.
11. Reinstall the parts and re-start your mower.

Why Won’t My Electric Lawn Mower Start?

Whether you have a corded or cordless lawn mower, the three causes of problems with starting it are as follows:

1. Power Supply Issues

If you have a long-cabled corded lawn mower that won’t start, the first thing you need to do is check if it’s still connected to your electrical outlet.

It isn’t uncommon for it to get pulled out while you’re busy cutting grass.

It’s also possible that your home’s electrical outlet is the one with issues, so you also need to check it.

To do so, try plugging in a cellphone charger, a lamp, or any small appliances or devices.

If they don’t work, check for blown-off fuses or breakers. Replace them if you have the right skills or call an electrician.

You can also check for frayed or broken wires, making sure you’re wearing gloves for electrical safety.

Again, repair or replace them if you have the right skills or call an electrician.

On the other hand, if you have battery-operated mowers, ensure that the battery is fully charged.

You must also check whether the battery is still working and require replacement.

2. Full Cutting Bag

Your lawn mower might not start because the collection bag is full of cuttings or clippings.

Apparently, all you have to do is empty its content.

3. Engaged Safety Mechanism

Some lawn mower models have safety mechanisms to prevent kids from starting the equipment accidentally.

Thus, an engaged safety mechanism won’t start.

Look for the button or lever and then disengage.

Why Wont My Lawn Mower Start?

There are more reasons your lawn mower won’t start, apart from what we discussed above.

Before checking and troubleshooting, make sure your lawn mower is turned off and that you read the user’s manual.

If you checked everything that we discussed and tried troubleshooting but to no avail, it’s best to bring your equipment to a professional.