17 Reasons a Big Dog Zero Turn Mower Won’t Start (SOLVED)

A Big Dog zero-turn mower won’t start when a spark plug isn’t able to ignite an air and fuel mixture for combustion.

This may be due to a loose spark plug wire, clogged air filter, bad fuel pump, plugged fuel filter, dirty carburetor, weak battery, corrosion on the electrical components, bad safety switches, or old gas. 

Take caution when troubleshooting and repairing your Big Dog starting problem. Remove the ignition key, remove the spark plug wires, and wait for all parts to stop moving before performing repairs.

Follow additional safety procedures found in your operator’s manual.

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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.

Reasons Your Big Dog Mower Won’t Start (Causes & Solutions)

1. Empty Fuel Tank

You may not realize the tank is low on gas because you developed a fuel leak, the gas gauge isn’t working, or you just simply forgot the last time you added fuel to the tank.

SOLUTION: Fill the fuel tank with fresh fuel.

• Inspect the fuel system and repair any leaks.
• Make sure the fuel gauge is working.
• Add gas with a minimum 87 octane rating and no more than 10% ethanol content.

Read more on choosing the right gas for your Big Dog mower here. 

2. Bad or Old Fuel

Gas begins to deteriorate, break down, and become less effective after about 30 days.

Ethanol, an alternative fuel added to most gas, naturally attracts moisture to the fuel system. This leaves behind varnish and gummy residue that clogs the fuel passageways including the fuel lines, filter, and carburetor.

Tips to avoid the effects of old fuel in your Big Dog mower:

• Purchase fresh gas with a minimum 87 octane rating and a minimum of 10% ethanol content.
• Consume fuel within 30 days.
• Use a fuel additive to make gas stable so it last longer before it breaks down. Read more about fuel additives here.
• Store fuel in a dry location away from moisture.

SOLUTION: Remove the old fuel from the fuel tank and refill it with fresh fuel and a fuel additive to clean the fuel system.

• Wipe around the fuel cap to remove loose dirt and debris. Remove the cap.
• Using a fuel siphon pump or another method, drain fuel into an approved fuel container.
• Add a fuel additive like Sea Foam Motor Treatment to your container of fresh gas. This is to help clean the fuel system, remove moisture, and keep the gas stable longer.
• If you are able to start the mower, start and allow the Big Dog to run so the treated fuel mixture works its way through the fuel system.
• If it doesn’t start, keep troubleshooting with the items below. Let the mower run for a while once you are able to start it.

3. Bad Fuel Cap

The fuel tank must have a vent allowing air to enter the fuel tank as fuel is consumed. When the vent becomes plugged, vacuum forms inside the tank preventing fuel from flowing out of the tank and to the carburetor.

The fuel tank vents through the gas cap on a Big Dog lawn mower.

SOLUTION: If your mower stopped running and won’t restart, determine whether you have a vacuum problem using a pressure gauge or follow these simple steps if you don’t have a gauge:

• Wipe around the fuel cap to remove loose dirt and debris.
• Loosen the fuel cap to allow air to enter the fuel tank.
• Attempt to start your mower.
  • If it doesn’t start, tighten the fuel cap and continue to troubleshoot other items that may cause your starting problem.
  • If it does start, tighten the fuel cap and allow your mower to continue to run. You’re trying to replicate the problem where your mower begins to run sluggish and dies due to a vacuum problem.
• If your mower started once you loosened the cap, but died after you tightened it and allowed it to run for a while, there’s a good chance the cap is no longer venting.

Replace a gas cap that is no longer venting with a new fuel cap.

4. Bad Spark Plug or Loose Connection

Another reason your Big Dog won’t run may be due to a bad spark plug connection or damaged spark plug. A plug that has carbon buildup or oil on the tip can foul out causing your engine to misfire and not start.

SOLUTION: Replace a very dirty or damaged spark plug. You may have two spark plugs on your engine model.

• Remove the spark plug wire (boot).
• Wipe around the spark plug to remove loose dirt.
• Use a spark plug socket wrench to remove the plug. Depending on your engine model, you’ll need a 3/4″ or 5/8″ socket.
• Inspect the plug for damage, wearing, or a dark tip from carbon buildup. If you find these conditions, it’s best to replace the spark plug with a new one.
• You can also clean it with a wire brush if it’s lightly dirty and in good condition.
• Check the spark plug gap to ensure it is at the engine manufacturer’s specifications.
• Install the good spark plug.
• Attach the spark plug wire. Make sure you remove the wire(s) if you are making more repairs.

I choose to replace the spark plugs when they are dirty or may inhibit the performance I receive from my zero turn. It’s an inexpensive maintenance item that will cause issues if its not in good working condition.

Spark plug(s) should be replaced annually.

5. Plugged Air Filter

The engine in your Big Dog requires air to run. When your air filter gets very dirty, it can starve the engine of air because sufficient air will no longer be able to pass through the filter.

When the airflow is blocked by your air filter the engine must find air to continue to run. It may overheat and draw what air it can find from the crankcase which can cause extensive damage to the engine.

The air filter is a maintenance item that should be replaced annually and cleaned several times throughout the mowing season.

SOLUTION: Inspect and replace an air filter that is very dirty or damaged. Clean a filter if it is lightly dirty using the steps below.

Refer to your operator’s manual if you are unsure of the type of filter on your model and its cleaning instructions.

Clean a Big Dog PAPER air filter:

• Remove the air filter from the housing.
• Wipe out any dirt remaining in the air filter housing and cover. Don’t allow dirt to fall into the air intake.
• Inspect the paper air filter. Tap the filter to loosen dirt so it falls from the filter. You should be able to see light through the filter when the filter is in good condition. However, If the filter is very dirty, damaged, or no longer seals the air intake sufficiently, replace it with a new one.
• Install a clean or new air filter.
• Reattach the air filter cover.

6. Clogged Fuel Filter

Your fuel filter is a line of defense to prevent dirt and debris from getting to the engine through the fuel system. Make sure the fuel that is running into the filter is also running out of the filter.

If it does not, you must replace it because it is most likely plugged preventing your Big Dog from starting.

SOLUTION: Replace the fuel filter using these steps:

• Shut off the fuel supply using the fuel shut-off valve or clamp the fuel line to stop the flow.
• Use needle nose pliers to remove the clamps and slide each end of the fuel filter out of the fuel lines.
• The filter may have a directional arrow showing which way the filter must be inserted into the fuel lines. The arrow must be pointed in the direction of fuel flow.
• Install the new filter into the lines and use the clamps to securely hold the fuel lines to the filter.

7. Clogged Fuel Line

Old fuel and dirt leave deposits that can clog your Big Dog mower’s fuel line.  

SOLUTION: Remove the fuel line, spray carburetor cleaner into the line, and use compressed air to blow air through the tube until the line is free of dirt and gummy residue. You can also replace it with a new fuel line. 

8. Bad Fuel Pump

The fuel pump exists to get fuel to the carburetor. When the fuel tank sits below the carburetor a pump is needed to help move the gas.

A fuel pump, just like any other mechanical part, can fail over time. A likely cause is due to old fuel deteriorating the pump components.

SOLUTION: To identify a failing fuel pump, first, inspect your vacuum fuel pump for cracks.

If you see fuel outside of the fuel pump or cracks in the pump, the pump will no longer be able to use the pressure off the crankcase to move fuel to the carburetor. 

Steps to identify a bad vacuum-style fuel pump:

• Make sure you are getting fuel to the inlet port on the pump before checking the pump. If you are not, check for a fuel restriction in the fuel line or fuel filter. Proceed once you are getting fuel to the pump.
• Shut off the fuel supply using the fuel shut-off valve or a clamp to pinch the fuel line to stop flow.
• Remove the fuel line from the carburetor and place it in a container to collect fuel.
• Start the mower and watch the flow coming out of the line into the container.
• You should see a steady or pulsating flow of fuel.
• Replace the fuel pump if there isn’t a good flow of fuel coming out of the line.

Without a good fuel pump, fuel will not get to the carburetor and your Big Dog mower will not start or run.

9. Clogged & Dirty Carburetor

The function of the carburetor is to regulate the amount of gas that mixes with air so your engine can start and create combustion. Carburetors can develop a crusty buildup and gummy deposits from using old fuel containing ethanol.

When the carburetor is no longer able to regulate the amount of fuel and air your engine receives, your Big Dog engine will run rough or it may not even start at all.

SOLUTION: If you are somewhat mechanical, you can try to clean the carburetor yourself, otherwise, bring it to your lawn mower repair shop. You can find steps for cleaning your Big Dog carburetor in this article. 

You may choose to replace the carburetor if it appears to be in very bad condition. 

10. Loose or Corroded Cables, Wiring, and Terminals

If your cables happen to be loose or your battery terminals show signs of corrosion, you need to tighten them and remove any corrosion you find.

Follow the cable off the positive cable to the solenoid and the cable from the solenoid to the starter. When these cables are not tight or have corrosion buildup, your mower may not start.

Continue to check all wiring and components on your Big Dog.

SOLUTION: Tighten the cables and make sure all wiring is securely attached to the mower components. Use a water and baking soda mixture to remove corrosion.

Make sure you remove the negative battery cable first followed by the positive cable.

11. Weak or Bad Battery

Your Big Dog lawn mower requires a charged battery to start. If the battery is weak, you must charge it to start. This is one of the many reasons a zero-turn won’t turn over or crank.

SOLUTION: Test your battery with a multimeter. You need a reading of about 12.7 volts. Charge your battery if it is lower than this level. You can find more information on charging a Big Dog battery and why it keeps dying here.

If your battery does not hold a charge, you will need to replace it with a new battery. 

12. Bad Safety Switch

Your lawn mower may use several safety switches in its operator’s presence control system. The switches are designed to kill the engine when the operator leaves the seat.

A faulty switch may not recognize when the operator is in or out of the seat causing your Big Dog not to start. 

SOLUTION: You can temporarily bypass the safety switch to identify a bad switch. Do not operate a mower without the safety switch installed for your safety. 

Always have safety switches installed and working on your equipment. Replace a bad switch. 

13. Bad Ignition Switch

You insert the key into your ignition switch and turn it only to find nothing happens. Your Big Dog mower does not start. The ignition switch can be the culprit. You can use a multimeter to test the ignition switch 

SOLUTION: Replace the switch if bad 

14. Bad Ignition Coil

The ignition coil provides voltage to the spark plug so it can fire and start the engine. The engine will not start if the spark plug isn’t able to fire.  

SOLUTION: After you verified your spark plug is in good condition, check the continuity of your ignition coil using an ohm meter. Replace the ignition coil if you find a break in the continuity. 

15. Bad Starter Solenoid

When your Big Dog mower clicks and won’t start, a bad starter solenoid is often the cause.

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 Big Dog mower solenoid may be bad is when a wire attached to your solenoid gets hot and begins to smoke or melt.

SOLUTION: Test your Big Dog mower solenoid by following the steps here. Replace your solenoid if it is found to be bad.

16. Faulty Charging System

While the charging system isn’t the main reason a Big Dog 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: If you believe the problem to be in your charging system, I suggest you allow a small engine mechanic to identify which part of the charging system is your problem.

Taking a guess at the problem and throwing parts at your mower can get pretty expensive.

17. Incorrect Operating Procedure

Big Dog has safety features that won’t allow your mower to start unless you follow its starting procedures.

SOLUTION: Refer to your Big Dog operating manual to ensure you are operating your lawn mower correctly, so you don’t set off the safety features that shut off your lawn mower or don’t allow it to start.

For example, on a Big Dog riding mower or zero-turn, the brake must be engaged and the PTO switch must be off for the engine to start.

Big Dog Starting Problems & Solutions (Quick Reference Chart)

Causes	Solutions
Empty Fuel Tank	Fill with fresh fuel. Big Dog mowers require gas with a minimum 87-octane rating and maximum 10% ethanol content.
Bad or Old Gasoline	Drain the old fuel. Fill with fresh fuel adding a fuel stabilizer that reduces moisture and cleans the fuel system.
Plugged Air Filter	Clean the filter by knocking dirt out of a paper air filter. If the filter is very dirty, dark in color, wet or damaged, you should replace it with a new filter.
Dirty or Damaged Spark Plug	Clean a dirty spark plug with a wire brush. Replace the plug with a new one if it is very dirty, has broken porcelain, or damaged electrode.
Plugged Fuel Filter	Replace a plugged fuel filter with a new filter. Make sure the arrow on the inline filter is installed and pointed in the direction of the fuel flow.
Plugged Fuel Line	Shut off the fuel supply and remove the fuel line from the mower. Use carburetor cleaner to loosen the clog and compressed air to remove it. Replace a line if you are unable to remove the restriction.
Bad Fuel Pump	Check fuel flow from the pump. Replace a bad fuel pump.
Dirty Carburetor	Remove the carburetor and clean it with a carburetor cleaner. You may need to rebuild it or replace it if cleaning alone does not work.
Bad Safety Switch	Replace a bad safety switch.
Loose or Corroded Cables Connections	Make sure the wires and cables are making a good connection. Remove any corrosion on the terminals and wires.
Weak or Bad Battery	Charge a weak battery. Replace a battery that will no longer hold a charge.
Faulty Ignition Switch	Replace a bad ignition switch.
Plugged or Faulty Fuel Cap	Replace a fuel cap that is no longer venting to allow air to pass to the tank.
Bad Ignition Coil	Replace a bad ignition coil if there is a break in continuity.
Bad Starter Solenoid	Test a Big Dog starter solenoid and replace it if bad.
Faulty Charging System	If the battery is good and will hold a charge, but the mower continually dies due to a dead battery and will not start, have a mechanic identify whether your problem lies with a component of the charging system.
Incorrect Starting Procedure	Follow starting procedures for the mower as there are safety switches that can prevent the mower from starting if not following the correct steps.