Many people will tell you that upgrading to a zero-turn lawn mower is a great idea. Undeniably, zero-turns are fast, have large deck options, and are great in tight spaces. However, they fail to tell you that zero-turn lawnmowers can go wrong in many different ways. So, before you pull out all your hair trying to start your mower, let’s figure out why your zero-turn mower won’t start and go over some common causes creating the problem.
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Reasons Your Zero-Turn Mower Won’t Start (Overview)
For a zero-turn lawnmower to start, a long list of components must be in proper working condition. Unfortunately, if any one or a combination of a few features fails, then your zero-turn mower’s engine will struggle to start or won’t start at all. Here are 16 potential reasons your zero-turn mower won’t start.
- No Fuel
- Bad Fuel
- Bad Spark Plug
- Bad Gas Cap
- Clogged Fuel Filter
- Dirty Fuel Lines
- Clogged Carburetor
- Bad Fuel Pump
- Dead Battery
- Loose Connections
- Bad Ignition Switch
- Bad Coil
- Bad Stator
- Faulty Starter Solenoid
- Faulty Safety Switch
- Wrong Starting Procedure
Common Reasons Why a Zero-Turn Mower Won’t Start (A Closer Look)
Generally, failure to start is one of the most common issues zero-turn lawnmowers face. Unfortunately, this could be down to many different issues that you’ll have to check through. With this in mind, here are 16 issues that I know of that could make starting your mower’s engine either hard or impossible. Let’s take a look.
No Fuel
Without a doubt, you’ll need to have fuel in your lawn mower if you want the engine to start. As simple as this sounds, I have wasted many precious minutes trying to figure out why my mower won’t start, only to find fuel was the missing piece. So, taking a quick look at the fuel tank and checking that your fuel is topped off is a good place to start. First, make sure you’re using the right fuel for your mower.
Bad Fuel
Does gas go bad? Well, unprotected gas will only last about 30 days before it begins to go bad. Now this should be an issue during the mowing season. But if you left gas in your mower over the winter months without any fuel stabilizer, it will be off come spring. When fuel is bad, it loses its combustibility. So, no matter how much you turn your lawn mower’s key, the engine isn’t going to start. A quick way to tell if your gas has gone bad is to compare it to fresh gas. Old gas oxidizes and turns a brownish color. So if you notice that the gas in your lawn mower is darker than fresh gas, you need to replace it.
Bad Spark Plug
Next on the list is a bad spark plug. A spark plug can develop several issues throughout its lifespan. For example, the center electrode wears down, and the plug can get covered in carbon deposits from burning fuel. When this happens, the spark plug won’t create the spark needed to ignite the fuel. So, test your mower’s spark plug to check that it is clean and gapped correctly and that the center electrode isn’t too worn.
Bad Gas Cap
Lawnmower gas caps are usually vented to release pressure as the mower uses more and more gas. So, if this vent is clogged or damaged, back pressure will form, trapping the gas in the tank and preventing the engine from starting. So take a close look at the vent and ensure it is unclogged and operating as it should. Sometimes the pressure created by clogged vents can cause the gas cap to become stuck.
Clogged or Dirty Air Filter
Now onto the next issue that could be preventing your lawn mower from starting: a clogged or dirty air filter. Now for the engine to create the required air to fuel mixture, there needs to be a certain amount of air allowed to enter the carburetor. So, if your carburetor can’t get enough air, the mix will be rich (too much fuel), and the engine may fail to start. So, inspect the air filter and check if it needs to be either cleaned or replaced. Usually, cleaning the lawn mower’s air filter will solve this issue. Worst case, you’ll just need to install a replacement.
Clogged or Dirty Fuel Filter
The fuel filter sits inline on the fuel delivery system to filter out imperfections and junk in the fuel. This could be stuff like grass clippings that made their way into the gas tank or microscopic impurities within the fuel, especially old fuel. Unfortunately, the fuel filter can only filter out so much junk until it becomes clogged, reducing the amount of fuel making its way to the carburetor. Lack of fuel makes the engine either run lean (too much air in the fuel mixture) or not at all. So, look at the fuel line between the gas tank and the fuel pump and check to see if it is discolored. The discoloration typically means the fuel filter is old and needs to be replaced.
Clogged or Dirty Fuel Lines
Just as the fuel filter can get clogged, so can the fuel lines. Now, this typically happens when something large like grass clipping or fuel gum blocks the fuel lines. So, just like a blocked fuel filter, a clogged fuel line limits gas from getting to the carburetor and prevents the engine from starting. So, to check if you have a clogged fuel line on your zero-turn mower, you’ll need to inspect the lines individually by removing them. Usually, you should be able to clean your mower’s fuel lines, but if they are in really bad condition, say they are cracked or split, then you need to install replacement fuel lines.
Clogged or Dirty Carburetor
The carburetor is the next component that can get in the way of fuel getting to the cylinder head. The carburetor, in basic terms, is responsible for providing a gas-air mixture at the required rate to the cylinder head for the spark plug to ignite. Because liquid gasoline isn’t flammable, the carburetor converts the gasoline and air into a vapor so that it can ignite. The gas-air mixture is sent through a tiny jet within the carburetor to produce the needed vapor. So, if the jet is blocked, the vapor can’t be produced, and the engine won’t start.
First, locate your lawn mower carburetor, and inspect it. Next, clean the carburetor and see if that resolves the problem. If the problem persists, the carburetor may be beyond cleaning and needs replacing.
Bad Fuel Pump
In order for the fuel to flow through the fuel system, you need to have an operating fuel pump. For example, most zero-turn lawnmowers use a pulse-style pump that takes a -/+ pressure from the overhead valve (OHV) to activate the fuel pump. This pressure makes a small diaphragm within the pump and pushes fuel from the gas tank to the carburetor. So, not only do you need reliable pressure from the OHV, but you also need a working diaphragm and clear passage for the fuel to flow.
As complicated as this sound, it’s pretty easy to test. Here’s a list of the steps:
- Remove the OHV pipe from the fuel pump.
- Crank over the engine.
- You should feel a strong pulsing pressure from the engine.
- Reconnect the OHV pipe and remove the outflow of the pump.
- Connect a spare length of pipe to the pump outflow connector and place the other end of the pipe in a fuel-safe container.
- Finally, crank the engine and inspect the flow of fuel.
If the flow is weak and sputters, you’ll need to either service or replace the pump. But first, you’ll need to make sure that the fuel filter, fuel line, and the volume of gas in the tank are all good, as any of these will impede the flow of fuel through the pump. Can you clean a fuel pump? Well, some you can, but most you can’t, as they are sealed units. So if you have a sealed fuel pump that is causing you an issue, then you’ll have to install a new lawn mower fuel pump.
Bad Battery
Your zero-turn lawn mower relies on an electric starter to fire up the engine. The battery is the first component in a long line of parts that makes this possible. So, you’ll need to make sure that your lawn mower battery has enough power to get your lawn mower running. A quick test with a battery tester should tell you how your battery is doing. Just remember that a battery needs to have enough volts to start an engine and the ability to produce the required cold cranking amps. So, be sure to test both the volts and amps. If you don’t have a tester, then you can always take the battery to a battery store such as Autozone and have them test the battery for you. If the battery is good, then all you’ll need to do is charge your lawn mower battery, and you should be good.
Loose or Dirty Connections
The electrical connections are next on the list of reasons why your zero-turn won’t start. To get power from the battery to the starter motor, you’ll need strong connections. A weak or loose connection will drastically reduce current flow through the electrical system, preventing the engine from turning and cranking the engine.
So you’ll want to inspect all the connections in the ignition system to make sure they are tight and not corroded or dirty. A good place to start is the connections to the battery, starter solenoid, starter motor, and ignition. Depending on the design, you may need to check a connection with safety switches. To get your mower starter, you will need to address anything that you find loose or corroded. By spending some time cleaning the lawn mower connections and making sure everything is secure and tight, you should be able to get your mower up and running.
Bad Ignition Switch
To tell your lawn mower that you want to start the engine, you turn the key to the start, then to the run position. Internally, the ignition switch makes several different electrical connections as you do this. For example, it first sends a current to the starter solenoid in the start position to connect the battery to the starter motor. Then the ignition stops the coil from grounding when you set the ignition to run. When switching the key to the off position, the coil grounds and stops the spark plug from generating a spark.
As you can see, the ignition switch is a complicated little component. Unfortunately, if the ignition is faulty, it won’t make the correct connections, and your zero-turn mower won’t start. So, grab a multimeter and test the mower’s ignition switch by checking each circuit. If you find a fault, you’ll need to install a new ignition switch.
Bad Coil
What is a lawn mower coil? Well, a coil is what makes a spark plug spark. For the spark plug to spark, a magnet attached to the flywheel passes over the coil as the engine runs and creates a charge. The spark plug acts as a ground, attracting the coil’s charge. When the charge reaches the tip of the spark plug, it creates a spark.
Inside the coil is a wire wrapped around a piece of metal, usually an iron core. Each pass of the magnet over the coil generates heat, which degrades the insulation of the internal wire over time. As this insulation breaks down, the wire can short-circuit. As a result, this shorting makes the coil burn out, stopping the coil from being able to produce the needed charge.
So what does this mean for you? Well, if the coil burns out, your lawn mower won’t start. But, unfortunately, it’s not so simple. Other issues can also prevent your mower from starting, like if the coil gap is wrong, the coil isn’t grounded, the magnets are bad, the flywheel isn’t aligned correctly, or the coil isn’t connected properly. So, you’ll need to check all of these things to make sure the coil is in working order and that it is making the spark plug spark.
Bad Stator
A stator works like a coil, producing a charge as it passes a magnet. But instead of sending a charge to the spark plug, it sends a charge back to the battery for charging. So, if you keep finding your lawn mower has a dead battery, you’ll want to check the charging system. Now, if your mower starts, you can test the output voltage (dynamic testing) of the stator to ensure it produces a charge. However, if you can’t get your mower to start, you’ll need to check the stator for resistance using a multimeter. Any type of stator will have a range of resistance through the stator, which you can test. For example, a stator may have a resistance range of 0.07-0.13 ohms. So if you test your stator and it is outside of its own specific range, you’ll need to replace the stator.
Faulty Starter Solenoid
The starter solenoid directly connects voltage from the battery to the starter motor when the ignition key switches to the start position. So as you turn your ignition key, a voltage is sent to the solenoid, which actuates the solenoid plunger, completing the connection. So, as long as the starter solenoid receives the required power to actuate and the internal plunger moves, the solenoid will work.
When you turn the key, you should hear your lawn mower click. This is the sound the plunger makes when moving inside the solenoid. If you don’t hear the clicking sound of the starter solenoid, then there is an issue. First, connect the starter solenoid directly to the battery to tell if it’s the starter solenoid or something else, like a bad connection. This will eliminate all other issues and let you know if it’s the solenoid at fault. So test your lawn mower’s starter solenoid and see if it’s why your lawn mower won’t start.
Faulty Safety Switch
All modern lawn mowers, including zero-turn mowers, have several different safety switches to keep the lawn mower and operator safe. For example, there is usually a safety switch under the seat to ensure that you only start the lawn mower when you are sitting in the seat. When engaged, these safety switches complete a circuit within your lawn mower’s electrical systems, making it possible to start your lawn mower.
If they are not engaged or damaged, then your zero-turn mower won’t start. An easy way to test your mower’s electrical connections is to use a multimeter set to continuity to check that each switch does, in fact, work. When a switch is ON/engaged, there should be continuity. When the switch is OFF/disengaged, there should be no continuity.
During this process, it’s worthwhile checking the wires going to the switch. Also, when you are checking any electrical component on your lawn mower, it’s a good idea just to check the wiring. On a few occasions, I thought a component was at fault when it was just the wiring. So all you might need to do to start your zero-turn is repair your mower’s electrical wiring.
Wrong Starting Procedure
Finally, using the wrong starting procedure could be why your zero-turn mower won’t start. For example, for most mowers to start, you need to be sitting in the seat with the brake engaged and the blades disengaged. Now if you try to start your lawn mower using the wrong procedure, say while the blades are engaged, then your lawn mower won’t start. The easiest thing to do in this situation is to check your manual for the correct starting procedure.
Fixing a Zero-Turn that Won’t Start (The Options)
As you can see, there are many different reasons your zero-turn lawn mower might not start, and there are many different possible solutions. For that reason, I’ve created a quick table summarizing the different components, tests to carry out, and fixes.
| Component | Test | Actions if at Fault |
|---|---|---|
| No Fuel | Check the gas tank | Fill the gas tank |
| Bad Gas | Test the gas quality | Remove the old gas and replace it with fresh gas. |
| Spark Plug | Check the spark plug for wear | Clean the spark plug Gap the spark plug Replace the spark plug |
| Gas Cap | Inspect the vent for clogs or damage | Clean the vent Replace the gas cap |
| Air Filter | Check the air filter for debris build-up | Clean the air filter Install a new air filter |
| Fuel Filter | Inspect the fuel filter for discoloration | Replace the fuel filter |
| Fuel Lines | Check the fuel lines for debris or cracks | Clean the fuel lines Replace the fuel lines |
| Carburetor | Inspect the jet for clogs Check the fuel float for dirt buildup | Clean the carburetor Remove and replace defective parts Install a new carburetor if needed |
| Fuel Pump | Check the OHV pipe Monitor the fuel flow | Restore +/- pressure Clean the fuel pump Replace the fuel pump |
| Battery | Test the battery with a multimeter | Charge the battery Replace the battery |
| Electrical Connections | Make sure the connections are tight Check the connections for dirt or corrosion | Tighten the connections Clean the connections |
| Ignition Switch | Check the ignition circuits with a multimeter | Replace the ignition if faulty |
| Coil | Test the coil Inspect the flywheel Check the coil gap Test the magnets | Align the flywheel Set the coil gap Repair the magnets Replace the bad coil |
| Stator | Check the stator for resistance using a multimeter | Replace the stator |
| Solenoid | Test the starter solenoid | Replace the solenoid |
| Safety Switches | Test the safety switches | Replace the safety switches |
| Starting Procedure | Check the manual | Implement the correct procedure |
