Lawn Mower Turning Over But Not Starting

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

How annoying is it when you’re trying to get your garden chores done but your lawn mower just isn’t cooperating? If you have found that your lawn mower won’t start, I can imagine that you’re pulling your hair out and asking why is my lawn mower turning over but not starting?

There are several reasons that your lawn mower spins but won’t start. It is usually either to do with the spark plugs or the fuel or air supply to the mower.

If you’re sitting frustrated in the garden with an uncooperative lawn mower right now, don’t worry. I’ve put together this guide for quick reference on how to troubleshoot and fix the problem. You’ll be up and running in no time!

When your lawn mower won’t start, you will need to take some time to address the issue and figure out what is causing it. There are a few different problems that could be at play here so I’ve broken them down into simple sections to help you work out what’s going on.

Bad Spark Plug

To get started, a lawn mower needs a good spark and if it isn’t getting enough of one, it isn’t going to fire up.

How To Fix It

Fortunately, this is a very simple problem to fix and can be done by removing the spark plug and giving it the once over. Make sure that it is clean and there aren’t any visible signs of damage. If there are, you will need to replace it.

Bad Spark Plug

Spark Plug Not Connected

The spark plug has a wire that needs to have good contact with the spark plug itself. You will see that there is a rubber cover and this needs to be properly fitted over the spark plug.

How To Fix It

Simply check the spark plug and ensure that the wire is properly connected and the rubber cover is in place. Make the necessary adjustments and try firing up the mower once again.

Fuel System Not Working

The fuel system contains a few elements that may cause problems when trying to get the lawn mower started.

You might want to check the fuel filter for any dirt or debris as well as making sure that there isn’t any old gas in the tank. Other issues could be that the fuel isn’t being adequately delivered to the engine which would certainly cause it not to start. You can check this using starter spray and if the mower fires up with this then fuel delivery is likely the root of the problem.

How To Fix It

If you notice that the fuel filter is clogged with debris or dirt then you will need to clean it. In some cases, it might be overly dirty and beyond repair in which case, you will need to replace it.

Where fuel has been left in the gas tank for an extended period of time, this will clog the carburetor which again, will need to be cleaned. You can do this using a carburetor cleaner. Just make sure to remove any old gas and replace it with new once you have done this.

Clogged Air Filter

The air filter needs to be kept clean in order that air can flow freely which aids in the process of combustion. However, this is a part of your mower that will get dirty from time to time so you need to keep an eye on this.

If there isn’t enough air getting to the engine then combustion won’t happen and the motor won’t start.

How To Fix It

Find the air filter on your lawn mower and take off its plastic cover. You may notice that the filter is covered in debris like grass or dirt so you will need to remove this. It is recommended that you clean the air filter every 25 hours of use but there will come a point where you need to replace it. Note that paper filters cannot be cleaned so once they become clogged, you’ll need to replace them regardless.

clogged air filter

Faulty Lock Out

Your lawn mower will have a safety sensor or a lock out that stops the engine from starting up accidentally. If this is faulty or the correct process hasn’t been followed, the mower won’t start.

How To Fix It

Check that you are following the correct process for operation. If you are and the lock out is still preventing the mower from firing up then you should contact the manufacturer. If your mower is still under warranty, they’ll fix the problem for you.

Choke Not Working Properly

Most modern lawn mowers have an auto choke but there are some that still feature a manual choke. When the mower’s engine is cold, it won’t start unless the choke is set correctly.

How To Fix It

If you’re trying to start a mower with a cold engine and you believe the choke may be the problem, simply set it to full and the engine should start without an issue.

Bad Gas

Before you do anything, be sure to check whether there is actually any gas in the mower. It sounds like I’m teaching you to suck eggs but it’s amazing how easy it is to take the mower out of the shed and forget to top it up with fuel.

If there is fuel in there, the problem could be related to this. When fuel is left in the mower for an extended period without the mower running, it can go bad. This can cause corrosion inside the mower and can lead to all kinds of problems.

How To Fix It

Siphon out any old gas and replace it with some fresh fuel. Be mindful not to mix old and new gas together as this isn’t going to do your mower any favors.

Finding The Issue

The issues I have discussed above are usually what will cause a problem. However, it isn’t always as simple as just looking at the mower and knowing what is causing it not to start. Sometimes you have to dig a little deeper.

The Gas Shot Test

The gas shot test is something that is commonly done on riding mowers. This is because, nine times out of ten, the issue will be related to fuel problems and this test is an excellent way to start diagnosing that. What’s more, it’s something that you can do at home so you won’t need to worry about hiring a professional.

Start by ensuring that you have fresh gas in the tank and then take out the air filter. Get some starter spray or a small amount of gas and put this into the carburetor. Go back and try to start the mower again. If you find that the lawn mower starts up or at least tries to start up then this tells you that it’s a fuelling fault.

Sometimes, this test will yield no results and the mower won’t start at all. In this case, you’re probably facing a spark plug issue.

Check The Choke

check the choke of lawn mower

After you have performed the gas shot test and determined that there is a fault with the fueling system then you will need to also check the choke.

The choke is a part of the mower that limits how much air gets into the carburetor. In turn this allows for better mixing of fuel and air. However, the choke is only needed when starting a cold engine and, as I mentioned earlier, you’ll need to make sure that the choke is set to full before trying to fire up the engine.

Additionally, make sure that the choke plate is functioning as it should. If it isn’t, you will need to adjust the cable into a fully closed position which should get things moving in the right direction.

Troubleshooting The Spark Plug

If you did the gas shot test and the mower still wouldn’t start then you’ve probably got a spark plug problem. Take the spark plug out and inspect it; this will tell you a lot about what’s going on in the deeper workings of the engine.

If the spark plug is wet then this could be a sign that too much fuel is being delivered to the engine and there may be flooding.

For spark plugs that are dry, this suggests that fuel isn’t being delivered which may mean there is a fault with the choke or the fuel system is blocked somewhere.

Finally, if you notice that the spark plug is oily and black, this might mean that there’s too much oil in the engine and some will need to be removed.

For the most part, keeping the spark plug clean will prevent issues here but do make sure to replace it when necessary. When you do this, it’s essential to make sure that you use the right spark plug for your mower or it won’t perform as expected and could even damage the mower.

Riding Mower Turning Over But Not Starting

Riding mowers may experience any of the problems that have already been discussed in this guide. However, there are a couple of other things you might need to look at.

Firstly, there could be a problem with the safety switch. Things like the emergency brake must make good contact otherwise the mower just won’t start up. In this case, it probably won’t even turn over.

But one of the most common issues here is simply that the switch isn’t clean. If it is dirty, the contacts won’t be able to make connections correctly and this is likely the cause of the problem. Give the switch a clean and see if it makes a difference.

You’re also going to want to check the seat switch. Move around in the seat and try to distribute your weight evenly, if the mower still won’t start, it’s likely that the seat switch is faulty.

If the emergency brake is faulty then, even when it is engaged, the mower won’t start. This is far from being a common issue but it’s worth checking everything just to be sure.

Final Thoughts

Have you noticed that your lawn mower spins but won’t start? If so then there could be a number of things causing this. It’s usually to do with the fuel or spark plug so it’s important to check everything over to help find out what’s causing the problem.

Most things can be easily fixed at home but if you are ever unsure, hire a professional who will be able to diagnose and fix the issue for you.

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Andrew Fisher

Andrew Fisher

Andrew is a dedicated father of three who really takes pride in his lawn and garden. You'll find Andrew behind the scenes of almost everything Edge Your Lawn produces. When he's not helping readers find all the information they need, he's in his backyard working on his lawn and garden landscaping. This year he hopes to build an outdoor deck and sort out his veg patches.