When it’s time to cut the grass, you want to be sure that your lawnmower works correctly. Unfortunately, sometimes when you turn the ignition, the engine turns over but doesn’t start. When that happens, it’s time to diagnose the problem so that you can fix it.
The most common reasons why a lawnmower will turn over but not start include bad gasoline in the tank, a dirty carburetor, a faulty spark plug, or a clogged air filter. Inspect each of these components to determine which one needs replacing. Usually, if the carburetor is to blame, you can clean it without having to install a new one.
Because there are so many potential issues, we will walk you through each one and show you how to fix it. You’ll have your mower up and running in no time!
Table of Contents
- Top 6 Reasons Why Your Lawnmower Turns Over But Doesn’t Start
- Problem 1: Bad Gasoline
- The Solution: Drain the Tank and Replace the Gas
- Problem 2: Clogged Air Filter
- The Solution: Replace the Air Filter
- Problem 3: Dirty Carburetor
- The Solution: Clean Your Carburetor
- Problem 4: Clogged Fuel Filter
- The Solution: Replace Your Fuel Filter
- Problem 5: Faulty Spark Plug
- The Solution: Replace Your Spark Plug
- Problem 6: Broken Flywheel Key
- The Solution: Replace the Flywheel Key
- Related Questions
Top 6 Reasons Why Your Lawnmower Turns Over But Doesn’t Start
Problem 1: Bad Gasoline
Contrary to what popular dystopian films may have you believe, gasoline doesn’t last very long. Unless you are putting stabilizers into it, fuel usually lasts between three and six months. So, if you’re trying to start your mower after an extended winter (and you left the gas inside the tank), it likely won’t combust correctly.
What happens is that the gasoline separates, and particles collect on the bottom of the tank. Water will also condense inside the mower, which dilutes the mixture and makes it less efficient. Because of these problems, we highly recommend adding fuel stabilizers to your lawnmower before putting it away for the winter or empty the tank.
The Solution: Drain the Tank and Replace the Gas
While adding new fuel might correct the issue, it’s far better to drain the tank first. Doing this will ensure that you have fresh, clean gasoline in the fuel line, the filter, and the carburetor, which makes your engine run far more efficiently.
The best way to drain gasoline is to use a siphon hose and a gas can. While you can use a standard hose and create suction with your mouth, doing so is far riskier since gasoline is highly toxic. When draining the tank, be sure that the gas can is lower than the mower. So, if you’re draining a push model, you will want to raise it on blocks or ramps before starting.
For the most part, you shouldn’t have to replace the fuel filter or the carburetor, but if changing the gasoline doesn’t help your lawnmower start, it might be necessary.
Problem 2: Clogged Air Filter
Gasoline is only one element necessary for combustion. The other is oxygen. The engine will draw oxygen in via the air filter, which mixes with the fuel inside the carburetor. So, if your filter is filthy and clogged, no air can get in, so no combustion can occur.
The Solution: Replace the Air Filter
Fortunately, lawnmower air filters are relatively inexpensive, so it shouldn’t be an issue to replace the whole thing. Unless you’re really trying to save some money, we don’t recommend trying to clean this piece. While you might be able to remove the larger pieces of dirt and debris, smaller particles are likely stuck within the fibers, which are impossible to remove.
The air filter will have a cover over it, so you will need a screwdriver or socket wrench to get it out. Depending on the type of mower you’re using, the location of the filter varies. Refer to your owner’s manual to find it.
Once the cover is off, all you have to do is pull the filter out and swap it for a new one. If necessary, check the model number on the old filter so that you can get an identical replacement. Unfortunately, air filters are not universal, so you have to make sure to buy one that is compatible with your mower’s make and model.
Problem 3: Dirty Carburetor
If the gasoline nor the filter are preventing your mower from starting, the likely culprit is where they are mixed – i.e., the carburetor. While modern vehicles abandoned this component back in the 80s because it was inefficient, almost all gas-powered lawnmowers use it.
The primary issue with the carburetor is that it can get clogged and gummed up with old gasoline residue. When the fuel evaporates, it leaves behind a sticky grime that can prevent various components from working correctly.
The Solution: Clean Your Carburetor
Thankfully, you should be able to clean this piece without having to replace it. Before starting, you will need to buy a carburetor cleaner. While you could try standard cleaning solutions, they are not designed to cut through the thick, gummy residue left behind by old gas. Carb cleaner does wonders, and it works far quicker.
You can find out more about how to clean your carburetor here. However, here are the broad steps to follow:
- Step One: Locate the Carb – Its position depends on the kind of mower you’re using.
- Step Two: Pinch the Fuel Line – You want to do this so that gas doesn’t flow into the carburetor while you’re cleaning it.
- Step Three: Remove the Bowl – This piece is held in place with a single bolt, and it collects the gas from the fuel line. Put a towel down beforehand to collect any drips.
- Step Four: Spray Carb Cleaner – Be sure to get inside each nook and cranny.
- Step Five: Scrub the Carburetor – Use a towel and a toothbrush to get into the smaller spaces.
Once the carb is clean, you can replace the bowl and any other pieces you had to remove to get to it. If this component is really filthy, you will need to remove it and soak it in cleaner. In extreme cases, you will have to buy a new carburetor and install it.
Problem 4: Clogged Fuel Filter
If your lawnmower uses a fuel filter to keep the gasoline fresh before mixing, it can get clogged with residue over time. Ideally, you should change this component at the start (or end) of every season so that you don’t run into problems. If it’s been a while since you’ve paid attention to the fuel filter, it is likely not allowing gas to flow through.
The Solution: Replace Your Fuel Filter
Fortunately, this is a relatively easy job and doesn’t require too many tools. Follow these steps to install a new filter.
- Step One: Locate the Filter – It will be located on the fuel line between the tank and the carburetor.
- Step Two: Clamp the Fuel Line – Make sure that no gas will leak out while you’re working. You only have to clamp the tank side of the line.
- Step Three: Release the Filter Clamps – There are two brackets on either side that hold the filter in place.
- Step Four: Remove the Old Filter – Be sure to put a towel down first, as there will be some gasoline inside.
- Step Five: Install the New Filter – Then reattach the clamps to hold it in place.
- Step Six: Un-Pinch the Fuel Line – This will allow gasoline to flow into the new filter.
- Step Seven: Run the Mower – You want to do this step to ensure that gas will flow through the system.
Problem 5: Faulty Spark Plug
Typically, if your engine is turning over but not engaging, the problem is likely with the fuel mixture. However, a faulty spark plug can sometimes allow the motor to turn over, but it won’t ignite the combustion correctly, so the lawnmower doesn’t start.
The Solution: Replace Your Spark Plug
As with most maintenance issues, you want to be proactive about installing new components into your lawnmower. Ideally, you should replace the spark plug once a year. If you haven’t done this in a while, now is the perfect time to do so. You can find out how to change a spark plug here.
Problem 6: Broken Flywheel Key
The flywheel is one of the most crucial components of your mower’s engine, as it is what allows the engine to run smoothly. This piece turns the crankshaft and generates electricity to recharge the battery while the machine is active. Typically, the flywheel breaks if you run over an object (i.e., a rock). So, if your mower isn’t starting after colliding with something you shouldn’t have, this is the likely cause.
The Solution: Replace the Flywheel Key
This project is relatively complex, so we highly recommend taking your mower to a repair shop. If the crankshaft is bent or broken, it might be cheaper to buy a new machine. Again, this shouldn’t be the cause of a non-starting lawnmower unless you ran over something, so try the other repairs first.
What if my mower won’t start at all?
In that case, the battery or the starter motor is likely to blame. A bad spark plug can also prevent your mower from engaging at all.
What if my mower starts but then dies immediately?
Many of the same issues can cause that problem as well, including a bad carburetor, spark plug, or air filter. So, by running through this list, you should be able to take care of either issue.