Skip to Content

16 Reasons a John Deere Zero Turn Mower Won’t Start

When you own a zero-turn, you’re most likely going to run into a time when the mower won’t start.

A John Deere zero-turn won’t start due to a plugged fuel filter, clogged fuel line, dirty carburetor, bad gas cap, bad spark plug, bad starter solenoid, faulty switch, bad battery, plugged air filter, or wrong choke setting.

Keep reading for additional starting problems. Always remove the ignition key and spark plug wire before performing repairs.

John Deere zero turn won't start

This post may include affiliate links. Purchases made through these links may provide a commission for us, at no extra cost to you. As an Amazon Associate, we earn from qualifying purchases.

Follow all safety instructions provided in your equipment operator’s manual before diagnosing, repairing, or operating. Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.

Other helpful articles for your John Deere starting problem:

Reasons a John Deere Zero Turn Mower Won’t Start

1. Empty Fuel Tank

You may have a faulty fuel gauge or you may have developed a fuel leak that can cause you to run out of fuel sooner than usual. You may have an empty tank simply because you forgot to check the fuel tank level before you started to mow.

I only mention this obvious cause of a starting problem just in case you skipped over checking the fuel level and moved on to looking at one of the many other items that can affect your starting issue.

SOLUTION: Check the fuel system to make sure you haven’t developed a fuel leak. If you find a leak, repair it or replace the faulty component. Add fresh fuel to the fuel tank.

2. Wrong or Old Gas

Correct Gas

Using the right fuel and keeping it fresh is essential for the mower to run well. Old gas is often the main culprit when a zero-turn starts running sluggishly, won’t start, or dies after running.

Most gasoline you find today includes ethanol. This is an alternative fuel added to gas to be more environmentally friendly because it is developed from plants.

Ethanol naturally attracts moisture from the air to the fuel system which is harmful to the small engine on your mower.

The water and ethanol mixture leaves behind varnish that restricts fuel flow and corrodes components that can keep the mower from starting.

Because ethanol has negative effects on a zero-turn engine and fuel system, always use gas with low ethanol levels or fuel that is ethanol-free. Gas with high ethanol levels can cause significant engine damage.

John Deere gas-powered zero-turns require unleaded gas with a minimum 87-octane rating and maximum 10% ethanol content. Read more about choosing the best gas for your zero-turn here.

Only Use Fresh Gasoline

Because gasoline begins to break down and becomes less effective as soon as 30 days, it is important to purchase gas and consume it within this time.

If you purchased more gas than you can consume within 30 days, use a fuel additive like Sea Foam Motor Treatment to stabilize the gas so it lasts a little longer.

I love this product! I actually add it to the fuel for all of my small engine products as added protection to the fuel system and engine. Read more about the advantages of adding Sea Foam to the fuel tank here.

SOLUTION: When you find you filled the fuel tank with the wrong fuel or the fuel is old, you must drain the fuel tank. A manual siphon pump is an inexpensive tool that works well to drain the tank.

Add fresh gas and a fuel additive to clean the fuel system, reduce moisture, and stabilize the fuel.

3. Plugged Fuel Filter

You will find a fuel filter inserted between the fuel lines to keep dirt from entering the fuel system. When the filter becomes plugged because it isn’t regularly replaced, the amount of fuel that passes through the filter is reduced.

The engine may not receive enough fuel for combustion. The fuel filter is a maintenance part that should be replaced annually.

SOLUTION: A clogged fuel filter must be replaced with a new one. Make sure you install it correctly with the arrow on the filter pointed in the direction of the fuel flow.

4. Clogged Fuel Line

The sticky deposits left behind by old fuel can get stuck in the fuel lines. This narrows the opening in the line restricting fuel flow.

SOLUTION: Once you find a clogged line, try to remove the blockage. To do this, remove the line from your mower.

Spray carburetor cleaner into the line to try to loosen the blockage. Follow the carb cleaner with compressed air blown into the line to remove the clog.

If you are unable to dislodge the clog, Purchase a new fuel line making sure you get the right diameter and length of the fuel line.

5. Bad Fuel Pump

The fuel pump on your zero-turn may be causing it to not start. The function of the fuel pump is to work against gravity to move fuel to the carburetor.

When it fails, the carburetor doesn’t receive the fuel it needs and the engine is unable to start. A carburetor failing due to old fuel is common.

Most John Deere zero-turn mowers use a vacuum-style fuel pump. Over time, fuel can cause your fuel pump to degrade.

For a pump that is no longer able to use the engine vacuum to draw fuel out of the fuel tank so it gets to the carburetor, the pump must be replaced.

If the fuel pump is leaking fuel, you must replace it. When you can’t see any visible signs of damage to your pump, perform a couple of tests to identify a pump problem:

  • Shut off your fuel supply using the fuel shut-off valve under your fuel tank or use clamps to pinch the fuel line to stop the flow.
  • Remove the hose from the inlet port on the pump. Place it in a container placed lower than the fuel tank so fuel can flow into the container using gravity. This step is to confirm your fuel pump is getting the fuel.
  • Start your fuel flow. If you are getting flow into the container, you have confirmed you are getting fuel flow to the pump. If you are not, you have a fuel restriction you need to locate prior to the pump.
  • Shut off the fuel flow. Replace the hose on the inlet port.
  • Remove the hose from the carburetor and place it in a container so you can confirm the condition of your fuel pump.
  • Start your fuel flow and start your engine. Watch for a steady or pulsating flow of fuel out of the fuel line.
  • Once your test is done shut off your mower and reattach your fuel hose to the carburetor.

SOLUTION: Replace the fuel pump if you are not receiving a constant or pulsating flow out of the pump.

6. Dirty Carburetor

A dirty carburetor can be the reason your John Deere zero-turn will not start and run. When the carburetor can’t regulate the amount of air and fuel the engine receives the engine will fail to start.

Old fuel often plays a role in a carburetor failure. This is because old fuel clogs the fuel passages restricting fuel flow. It can also leave behind varnish that causes internal parts to stick and no longer function.

When your carburetor does not work properly, you will have to clean the carburetor and replace any stuck or damaged parts that are unable to be cleaned.

SOLUTION: I have listed steps for cleaning your carburetor here. Follow these if you have a little mechanical ability and are comfortable working with small parts.

If you do not want to attempt cleaning or rebuilding your carburetor, you can take your mower to your small engine repair shop to be cleaned or you can replace it with a new carburetor assembly.

7. Bad Gas Cap

The fuel tank must be able to vent allowing air to pass into the tank. When there isn’t a vent, the tank forms a vacuum keeping fuel from leaving the fuel tank and getting to the carburetor.

On a John Deere zero-turn, the tank vents through the fuel cap so the air pressure in the tank is equal to the air pressure outside of the tank.

You may be able to identify a bad gas cap by running your zero turn with and without the cap. If your zero-turn won’t start with the cap in place, loosen the cap to allow air in the fuel tank. You may hear a vacuum release.

If you are able to start the mower after loosening the cap, you may have a gas cap venting problem.

Tighten the cap and run the mower to see if you can recreate the issue where it shuts off and then won’t restart until the fuel cap is loosened.

SOLUTION: Replace the fuel cap.

8. Bad Spark Plug

Fouled spark plugs or plugs with broke porcelain or worn electrodes can cause intermittent spark issues that may prevent the engine from starting.

Check your spark plug to ensure they are in good condition. Make sure the spark plug wires are securely attached and the electrode gap is set to the manufacturer’s specifications.

SOLUTION: Remove your spark plug and inspect it for signs of carbon buildup or a cracked porcelain insulator. Replace with a new spark plug(s) if they are damaged, worn, or very dark in color.

If the spark plug(s) is in good condition, clean the tip with a small wire brush. Make sure the spark plugs are correctly gapped and the wires are secure.

9. Plugged Air Filter

An air filter is installed on your mower to keep dirt from entering the air intake and wearing the engine. When the filter isn’t cleaned regularly or replaced, the mower may not start.

I recommend replacing the air filter annually and checking its condition regularly through the mowing season. If you find the filter is in good condition, clean it.

However, if it is very dirty or damaged, it’s best to replace it with a new one.

SOLUTION: Check and clean the air filter. If the air filter is so bad that it’s keeping your John Deere from starting, you should install a new one.

Clean a paper air filter:

  • Remove the air filter from the filter housing.
  • Don’t let any dirt fall into the air intake. Wipe out any excess dirt that remains in the filter housing and filter cap with a dry cloth.
  • Tap the air filter against a solid surface to knock as much dirt loose as possible and allow it to fall out of the filter.
  • Hold the filter up to a light source and check for light shining through the paper element.
  • Reuse the filter if you can see light. Replace your filter with a new filter if you cannot see light, it is extremely dirty, or the filter is damaged.
  • Install the air filter.

10. Loose Cables or Corroded Terminals, Wiring, or Components

There can be a break in continuity when the battery cables, wiring, and electrical components are loose or corroded.

SOLUTION: Remove any corrosion you find. To do this, disconnect the battery and remove the corroded components.

Use a baking soda solution (2 cups of water mixed with 3 heaping tablespoons of baking soda) or cola to remove the corrosion along with a small metal brush.

Then, make sure all wiring and components are securely installed making good connections.

11. Weak or Bad Battery

When the battery is weak or dead, it won’t provide the power needed to turn over the engine. You’ll need to charge a weak battery and replace it with a new one if it isn’t able to hold a charge.

SOLUTION: Test your zero-turn battery with a multimeter. If your reading is less than 12.7 volts, place your battery on a battery charger. Read more about the steps and items needed to charge your John Deere battery here.

12. Bad Safety Switch

Your zero-turn has an operator presence control system installed to keep you safe. A safety switch can be defective and cause your zero-turn to fail to start.

SOLUTION: Test your switches using a multimeter. You can also temporarily bypass a safety switch to identify a bad switch, but only do this for troubleshooting purposes.

Never operate a mower without the safety switchNever run a mower when a safety switch is bypassed. A safety switch can save you from serious injury and you never know when you’re going to need it.

13. Bad Ignition Switch

The ignition switch could be the problem when you insert the key and find it fails to start.

Check the switch using a multimeter to check continuity to determine if the ignition switch is the problem. To do this, look for the prongs mark B for Battery and S for Starter Solenoid.

Insert the key and turn it to the start position. With the multimeter set to measure resistance, touch one probe to the B prong and the other probe to the S prong.

A good ignition key switch will measure resistance near 0 ohms. A bad ignition key switch will measure infinite resistance and will need to be replaced.

SOLUTION: Replace the ignition switch if it is bad.

14. Bad Starter Solenoid

A lawn mower solenoid is an electromagnetic switch that is like an on-off switch that actuates the starter motor to turn over the engine. A click or hum when turning your ignition key is an indication to check your solenoid.

Another indication your solenoid may be bad is when a wire attached to your solenoid gets hot and begins to smoke or melt.

SOLUTION: Test your John Deere solenoid by following the steps here. Replace your solenoid if it is found to be bad.

15. Faulty Charging System

While the charging system isn’t the main reason a John Deere zero-turn mower won’t start, it can contribute to a weak battery that prevents the mower from starting.

When the charging system fails to charge the battery, the battery may not be able to start the mower the next time you go to use it.

A bad stator or alternator can be the problem along with several other electrical parts. Read this article to test your charging system here using an ohmmeter. 

SOLUTION: Once you identify the problem that lies in your charging system, my advice to you is to bring it to your local John Deere mower dealership for troubleshooting.

There are many components that make up the charging system. Without the experience, you will most likely throw parts at your mower hoping to find the problem.

Electric parts on your lawn mower can be expensive. Most likely, electric parts are non-returnable. So, if you find the expensive part you bought is not the problem, you are stuck with it.

16. Incorrect Operating Procedure / Wrong Choke Setting

There are several starting procedures you will need to follow in order to start your zero-turn.

Check the Choke Setting

The choke is used to restrict airflow when starting a cold engine. When the choke lever isn’t in the right position, the mower can fail to start.

  • Starting a cold John Deere zero-turn:
    • Place the choke lever in the full choke position.
    • Place the throttle halfway between slow and fast throttle positions.
    • Turn the key to the start position and then release it once the engine starts.
    • Adjust the choke lever to the off position.
    • Allow the engine to idle at half throttle for a few minutes before adjusting to full throttle to begin mowing.

Ensure you are following the steps of the safety interlock system:

The safety interlock system is designed to keep you safe. Your mower won’t start if you don’t satisfy the safety requirements required to use the mower.

Check these safety measures are met to start the zero turn:

  • Sit in the operator’s seat.
  • Place the steering control levers in the outward position to engage the brake. If you have a separate brake lever, engage the brake.
  • Make sure the PTO is off.

SOLUTION: Follow the steps above to start your zero-turn. This includes following the safety starting procedures and having the choke in the correct position.