Why is My Lawn Mower Turning Over But Not Starting? (Causes + Fixes)

Whether you are a weekend warrior or a seasoned pro, you are likely to encounter a lawn mower turning over but not starting at some point. This problem can be attributed to a few different causes, and it may well be a very easy fix. Let’s hope that’s the case for you!

Why is My Lawn Mower Turning Over But Not Starting?

This kind of problem is commonly related to either the air, fuel, or spark supply systems within the motor. The internal combustion engine will need all three of these elements to run, so if one of them is not sufficient you may see your lawn mower turning over but not starting. Luckily, all three have relatively easy parts for us to check and troubleshoot.

Potential Causes of a Lawn Mower That Turns Over But Doesn’t Start

If you have been asking yourself “Why is My Lawn Mower Turning Over but Not Starting?”, you may want to check for the following to determine the cause.

Bad Spark Plug

If your mower isn’t getting enough of a spark for the ignition to take place, it may cause this problem. Take out the spark plug and check the spark element is intact and clean. A bad spark plug is an easy fix.

Spark Plug Wire Not Connected

While checking your plug, ensure that the spark plug wire is making good contact with the end of the spark plug. Ensure that the rubber cover is securely over the spark plug.

Dirty Air Filter

An air filter that’s not letting enough air into the motor can inhibit combustion. Locate the air filter on your mower and remove the plastic cover. If the filter is covered in dirt, grass, or some other contaminant, this may be the reason for your lawn mower turning over but not starting. The engine needs to be provided with enough air for the combustion process to work.

Fuel System Not Working

There are a few components in the fuel system that could be causing the problem. If gas has been left in the mower without running for an extended period, it may have gummed up the carburetor. You can also check the fuel filter, and if it is full of debris, or the clear container around the fuel filter is completely dirty, this could be contributing to the problem. To test the fuel system, you must rule out the other two parts of the equation. If the air filter is clean and the spark plug is fully intact, try spraying some starter fluid directly into the chamber with the air filter off the mower. If the mower starts with this method, or starts and then stalls, that tells you that it is a problem with the fuel delivery to the motor.

How to Fix a Mower That Turns Over But Doesn’t Start

Fixing a Bad Spark Plug

If you have checked and determined you have a bad spark plug that may be the cause of your problem, you will need to either clean or replace the plug. Figure out which option is right for your mower by checking out the condition of the electrode, the ceramic coating, and the terminal that contacts the wire.

If the coating is cracked or the electrode is burnt, shortened, or missing, this will likely be the cause of your problem. You will want to replace the plug. If you find that the spark plug is just dirty on the tip, preventing a proper spark or connection with the wire, you may be able to clean it with a small brush and a light solvent.

Fixing a Spark Plug Wire Not Connected

If you find that the wire which connects your spark plug to the starting mechanism is not making contact, that could also be causing your problem. To fix this, you may only have to push the rubber shroud down around the plug so that it’s tighter. You can look inside the shroud and check that the wire is showing and has enough exposed to make contact. If the rubber shroud is ripped or worn out, you may need to replace the spark plug wire or shroud.

Fixing a Dirty Air Filter

If you have checked your air filter and discovered that it is covered with sand, dirt, grass, leaves or anything of the sort, you will need to blow it out for it to start working properly. Try tapping the air filter on a solid surface upside-down to get the large debris off. If you have an air compressor, stick the nozzle inside the filter and blow out. This will release a lot of the fine particulates trapped in the filter. If neither method solves the problem, it may be time for a new air filter.

Fixing a Fuel System That’s Not Working

If you have discovered a very dirty fuel filter, you may be able to replace this easily by yourself. You will have to find the right part for your mower and acquire it. The fuel filter is easily changed by releasing the clamps at both sides and connecting the new one the same way. Use a bucket to catch any fuel that runs out of the lines when disconnected. If the fuel filter is fine and you have ruled out any other parts of the ignition system, the carburetor may be the place to look next. Your carb may be gummed up, especially if the mower hasn’t been run in a while. If you suspect this is the case, you can either replace the carburetor or try and clean it. Cleaning a carburetor is an in-depth process and deciding whether to do this or leave it to a pro depends on how ambitious you are. If you decide to take it apart, make sure and take a picture or draw a diagram to remember where every part goes.

Riding Mowers That Turn Over But Don’t Start

Maybe you are asking yourself “Why is My Riding Mower Turning Over but Not Starting?” This may be due to any of the causes I’ve outlined above, but there are also a couple of additional things to check if you have a riding mower.

Safety Switch

Usually, if a safety switch such as the seat or emergency brake is not making contact, the mower will not even turn over. There is, however, a small chance that a switch may be working intermittently if it is dirty, or the contacts are not able to meet properly. This may cause your riding mower to turn over but not start. It is worthwhile to check the safety switches if the above fixes have not worked for you.

Check that the seat switch is working by re-distributing your weight over different parts of the seat and trying to start the mower. If all else is in working order and it still wont start, the switch under your seat may be bad.

Next, check that the emergency brake switch is making contact, if it is faulty, it will prevent the mower from starting even when the emergency brake is engaged. These causes are uncommon but may possibly be your cause if everything else is working properly.