Common Zero Turn Problems: How to Fix Them


Owning a zero turn lawn mower doesn’t come without its problems. Owners must accept the fact that some item on their zero turn will fail after time. With a good maintenance routine, you can prevent some of these problems. However, if you own the same zero turn long enough, components will eventually begin to wear and fail.  

Some of the most common zero turn problems and owner complaints are: 

  • Zero turn won’t start 
  • Zero turn dies when mowing 
  • Zero turn smokes 
  • Zero turn hydrostatic transmission is weak 
  • Zero turn won’t drive straight 

Keep reading and I’ll explain how to diagnose and fix these common issues. 

How to fix common zero turn mower problems

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Zero Turn Lawn Mower Problems 

Zero Turn Won’t Start 

Your zero turn lawn mower may not start because of fuel system problems such as a bad fuel, dirty carburetor, or a bad fuel pump. A bad spark plug, battery, safety switch and ignition switch can also cause your zero turn not to start.  

Bad Spark Plug in Your Zero Turn 

If your zero turn mower doesn’t start, your spark plug may be bad. However, if your lawn mower tries to start and turns over, the cause of your lawn mower starting probably doesn’t have anything to do with the spark plug since the engine turning over indicates you have spark. 

FIX 

  • Remove the spark plug boots and the spark plugs. 
  • Inspect the plug for dark deposits or cracked porcelain. The color of your plug should be amber in color. If it appears darker then this, your spark plug should be replaced with a new one. 
  • Replace your spark plug and make sure you gap the plug according to your manufacturer’s recommendations. 
  • Reattach the spark plug boot . 

No Gas in the Fuel Tank 

I’m not joking when I listed “no gas in the fuel tank”. I once had a customer so mad at me for not running to his place on a Saturday evening to repair a mower that wasn’t running. Come Monday morning, I checked the fuel tank and found the reason for his zero turn not running was because he forgot to add gas to the fuel tank. Boy, did that customer apologize once I told him about the lack of gas. 

FIX 

  • Add fresh fuel to your gas tank. 

It’s a simple thing to forget, so it is worth mentioning. 

Bad Fuel Pump on Zero Turn 

A fuel pump is used to pump fuel to the carburetor. The fuel pump has an inlet and outlet port where the fuel is come into and exits the fuel pump. There is a third port that is connected to a fitting off of the crankcase that creates the pressure the pump requires to function.

FIX

  • Inspect the fuel pump for cracks or fuel leaking around the pump. If you find cracks the fuel pump will no longer be able to hold pressure. You must install a new fuel pump.
  • Make sure you are getting fuel from the fuel tank to the fuel pump. Turn off the fuel valve or use a clamp to stop the flow of fuel. Disconnect the fuel line from the inlet port on the fuel pump. Place the line in a container that sits lower than the fuel tank. Unclamp or turn on the fuel valve and check to make sure fuel is flowing out of the tube. If you are not getting fuel, check for blocked fuel lines or a plugged filter.
  • Once you have verified you are getting fuel to the fuel pump, reinstall the fuel line to the inlet port on the fuel pump. You will now need to verify the fuel pump is pumping fuel to the carburetor.
  • Remove the fuel line from the carburetor. Place the fuel line into a container. Start your lawn mower and watch to make sure you have a steady or pulsating flow of fuel coming out of your fuel line.
  • Replace your fuel pump if it fails to provide a flow of fuel out of the outlet port.

Dirty Carburetor on Your Zero Turn 

The carburetor is essential to regulate the amount of fuel and air mixture required to create a combustion. When your carburetor is dirty or gummed up, your carburetor is no longer able to regulate this mixture causing your lawn mower not to start or run terribly when it does start. 

FIX 

  • Clean your carburetor. Most of the time a carburetor can be cleaned. If you are mechanically inclined you can clean your carburetor using these steps in this article.  
  • Replace the carburetor if the buildup of dirt and residue left from ethanol cannot be removed adequately.  
  • If you are not mechanically inclined or you don’t want to tackle the job, you can have your local lawn mower repair shop clean your carburetor. 

Dead Battery in Zero Turn 

A dead battery can be the result of a bad battery that won’t hold a charge, loose connections or corroded terminals. 

FIX 

  • Inspect your battery terminals for corrosion. Clean your battery terminals by mixing 2 cups of water to about 3 rounded tablespoons of baking soda. Using a wire brush, scrub the battery terminals until rust and corrosion is removed. Replace the terminals if you are unable to get them clean. 
  • Make sure the battery connections are all securely in place.
  • Test the voltage of your battery to ensure it has at least 12.7 volts. If your battery does not, you will need to check to verify it will hold a charge. If it will not hold a charge, it must be replaced. 

You can find additional information on what is draining your battery and how test and charge your battery in my article here

Bad Safety Switch in Zero Turn 

Your lawn mower may use several safety switches in its operator’s presence control system. The switches are designed to kill the engine if the operator leaves the seat. A bad safety switch can cause your zero turn mower not to start because it can’t sense the operator. 

FIX 

  • Temporarily bypass the safety switch to identify a bad switch.  
  • Warning: Do not operate a mower without the safety switch installed for your safety. Many people get injured by mowers annually by rolling them or falling off the mower. 
      
  • Always have safety switches installed and working on your equipment. 
     
  • Replace a bad safety switch. 

Bad Ignition Switch  

You insert the key into your ignition switch and turn it only to find nothing happens. The switch may feel a little different when you insert the key or you are unable to turn the key. The ignition switch can be the culprit to your starting issue. 

FIX  

  • Test the switch using a multimeter.
      
  • Replace the ignition switch if you find it is bad. 

Faulty Charging System in Zero Turn 

The charging system on a zero turn charges the battery while it is running. When your charging system is not working, your battery will die. 

FIX 

  • Test your charging system following the instruction here
  • If you find the fault lies with your charging system, bring your mower to a lawn mower repair shop that has an experienced technician on site. There are several pricey parts that can affect your zero turn’s charging system. An experienced technician will be able to isolate the problem where the unexperienced homeowner will be throwing parts at their lawn mower hoping to get lucky with the repair. 

Zero Turn Loses Power and Dies While Mowing 

Bad Fuel in Your Zero Turn 

Bad fuel will cause you to have problems with your zero turn. Gas only lasts about 30 days before it begins to break down and become less effective. Ethanol used in today’s fuel will attract moisture from the air and begin to separate from gas overtime. Ethanol can cause corrosion to the fuel system and leave deposits that can gum up the fuel system.  

To read more about the effects of ethanol and the correct gas to use in your zero turn, read my article “This is the Type of Gas Lawn Mowers Use”. 

FIX 

  • Drain the fuel into an approved fuel storage container to be recycled. 
  • Flush the fuel tank to clean it. 
  • In another fuel container, mix fresh gas and Sea Foam fuel additive following the instruction on the bottle. Sea Foam not only stabilizes fuel, it also can be used a fuel system cleaner. 
  • Add fuel mixture to fuel tank and let run. If the mower doesn’t stay running, you may have a clog in the fuel lines or a dirty carburetor. Read on for more information on isolating this issue. 

Plugged Air Filter in Zero Turn 

Your zero turn engine draws clean air in through the air filter. When your air filter is very dirty and plugged, your lawn mower cannot get the air it needs to mix with fuel to allow the engine to run. 

FIX 

  • Clean a paper air filter by removing it from the air filter housing being careful not drop any dirt into the intake. 
  • Wipe any dirt out of the housing with a dry clean cloth. 
  • Tap the air filter against a solid surface to knock any loose dirt from the filter. 
  • Hold the filter up to the light to make sure you can see light through the paper element. 
  • If you cannot see light through all areas of the filter, you need to replace it with a new air filter. 
  • Replace the filter in the housing. 

For information on cleaning procedures for other types of air filters, ready my article, “Guide to Lawn Mower Filters”. 

Dirty or Broken Fins on Fan 

Zero turn mowers are designed to keep air circulation to cool the engine. Make sure the engine shrouds, heat shields and fans are clean and not broke. FIX: 

  • Clean engine shroud and remove to gain access to the fan.
     
  • Inspect the fan and clean any dirt or grass build up on the fan.
     
  • Replace the fan if you any fins have broken off or have become damaged.
     
  • Reinstall the engine shroud. 
  • Make sure heat shield is installed correctly.

Clogged Fuel Lines or Fuel Filter on Your Zero Turn

Deposits left from bad fuel can get stuck in your fuel lines or clog your fuel filter.  

FIX: 

  • Clamp or shut off the fuel valve (if your mower has a fuel valve) and check each section of fuel hose to make sure fuel is able to flow through the tube and the fuel filter. 
     
  • Place the end of the section of fuel hose you want to check into a container, unclamp or turn on the fuel valve to check for fuel flow. 
  • If you don’t have fuel running through the fuel line, use a can of compressed airOpens in a new tab. to blow air through the line. 
  • Fuel line can be purchased from AmazonOpens in a new tab.. Replace the line if you are unable to unclog the line or if the fuel lines appear dry and brittle. 
  • Replace your fuel filter if fuel is unable to pass through the filter or if the filter is cracked. 

Dirty Carburetor 

A dirty carburetor cannot only prevent your lawn mower from starting due to not being able to get air and fuel to create combustion in the engine, but it can also make it run rough and die when the air to fuel is not at the rate or mixture required. 

FIX: 

  • Clean your carburetor. Most of the time a carburetor can be cleaned. If you are mechanically inclined, you can clean your carburetor using these steps in this article.  
  • Replace the carburetor if the buildup of dirt and residue left from ethanol cannot be removed adequately.  

Zero Turn Smokes 

Some of the same reasons as mentioned above for your lawn mower shutting down while mowing can be found the reasons your lawn mower is smoking as well. 

Plugged Air Filter 

When your zero turn isn’t able to get fresh air through the air filter because it is plugged, it will try to find air where ever it can. This means it is possible for air and oil to be pulled out of the engine’s crankcase. The burning of this oil causes your engine to smoke. 

FIX 

  • Install a new air filter.
  • Not catching the plugged filter soon enough could result in additional engine damage. Keep reading for more information. 

Too Much Oil in the Crankcase 

Overfilling your crankcase doesn’t seem like it would be a big problem, but it can actually cause some significant damage. Too much oil can cause crankcase pressure to build causing oil to get into the cylinder and into the air intake through the valve train. 

The oil in the cylinder burns off, when the engine gets hot, and creates a smoke. 

FIX 

  • Drain engine oil until the oil level is at the manufacturer’s recommended level. You can often find the oil level gauge on the oil dipstick. 
  • You can drain the oil using one of these 5 methods: 
    • Loosen the drain plug letting a little oil seep out and then retighten.
    • Use an oil evacuator to vacuum out oil.
    • Use a turkey baster to suck a little oil out of the oil fill tube.
    • Unscrew the filter and use a rag to collect a little oil. Spin the filter back on the engine

Engine Oil Level is Low 

Not having enough engine oil in your zero turn can increase the amount of friction and heat buildup in the engine due to inefficient lubrication. The mower will build heat and begin burning up the small engine components creating your zero turn to smoke. 

FIX 

  • Try to add fresh engine oil to your engine to see if the smoking stops. 
  • Most of the time, it’s too late for this simple solution and you will have to replace your engine. It is important to keep checking your engine oil on your pre-mowing checklist

Internal Engine Problems – Piston Ring, Valve Train, Engine Gasket 

It’s hard to identify a specific internal engine problem without taking the engine apart. One thing you can check that will indicate an internal engine problem is checking for oil on the spark plug. Excessive oil on the plug will indicate a possible ring problem and a score inside the cylinder wall. 

When the cylinder wall becomes scored, the engine can bring oil into the combustion chamber and begin burning it. This will create a smoke while the engine is in use. 

Your smoking problem may also be due a bad valve train problem or bad engine gasket. In order to find a valve train issue, you will need to remove the cylinder head and perform a leak down test. It also can be difficult isolating a bad engine gasket.  

FIX:  

  • Have a small engine mechanic diagnose your engine damage to see if it is able to be repaired or must be replaced. 

Weak Zero Turn Hydrostatic Transmission 

There are simple things to check to make sure your hydrostatic transmission performs well and keeps your zero turn moving. You can check some of these items yourself.  

I recommend taking your lawn mower to your lawn mower dealership for repair when you experience these problems: 

  • Your hydraulic pump is leaking oil. 
  • Your mower moves when it is cold, but stops when it is warm. 

Bad Drive Belt on Hydraulic Pump on Zero Turn 

Inspect the drive belt to make sure it is positioned correctly on the pulleys and not worn or shiny in appearance. 

FIX 

  • Replace belt if it appears frayed or worn. Install the belt correctly and check the tensioner pulley if the belt came off of the pulley. 

Bad Zero Turn Tensioner Pulley 

The tensioner pulley keeps tension on the drive belt. The tensioner arm must be kept greased to allow it to move and not seize up. 

FIX 

  • Inspect the tensioner pulley. Grease the tensioner pulley arm and make sure it has movement.  
  • Replace the tensioner pulley and/or tensioner arm if either is found to be bad. 

Low or Old Oil in Zero Turn Hydrostatic Transmissions 

Consistent hydraulic oil changes at the intervals required by your manufacturer need to be followed. It’s crucial to the life of your transmission system to be running good clean hydraulic oil. It should be part of your pre-mowing checklist to check the hydraulic fluid level in your zero turn. 

Transmissions running bad hydro oil or are low on hydro oil can cause your zero turn transmission to seem weak when you are mowing. 

FIX: 

  • Change hydraulic oil according to your manufacture guidelines at the required intervals. Most manufacturers have a “break-in” period where the hydro oil needs to be changed earlier than the standard interval. 
  • Make sure the hydro fluid level is at the “Cold Full” level on the hydraulic reserve tank. Check the level when your hydraulic oil is not warm. Add more fluid to bring it to the correct level. 

Zero Turn Won’t Drive Straight 

It’s frustrating to always have to compensate for your zero turn pulling a little to the left or a little to the right. There are some simple adjustments you can make to get your zero turn to drive in a straight path when on flat ground. 

Incorrect Tire Pressure 

Unequal tire pressure in both drive tires can cause your zero turn to pull to one side. 

FIX

  • Check tire pressure and fill so both tires have the same amount of air pressure. 

Bad Dampners 

A dampner is like a little shock for your steering. A bad dampner can cause your mower to jerk to one side when moving forward.

FIX

  • Replace a bad dampner. 

Tracking Adjustment Needed 

Tracking adjustments are needed periodically when you find your lawn mower is no longer moving in a straight path forward. Adjusting the speed adjustment bolt allows you to change the speed the tire is moving. Turning the adjustment bolt counterclockwise will slow the speed of the wheel. 

FIX 

  • Locate your speed adjustment bolt which is typically located at the bottom of the lever you use to move your lawn mower forward. 
  • If your lawn mower veers off to the right you will want to adjust the opposite side (left side) adjustment bolt by loosening the nut, turning the adjustment bolt counterclockwise a ¼ turn, and retightening the nut. 
  • If your lawn mower veers off to the left you will want to adjust the opposite side (right side) adjustment bolt by loosening the nut, turning the adjustment bolt counterclockwise a ¼ turn, and retightening the nut. 
  • Test your mower by driving it forward on a flat surface. Make further adjustments if necessary.  

Perform Regular Maintenance on Your Zero Turn

Taking time to check your mower before each mowing and performing routine service on your zero turn will prevent some of these issues or allow you to catch the problems before they develop into costly repairs. See my article on servicing your zero turn for a list of items you need to check when performing routine maintenance.

Powered Equipment Team

We're just a guy and a girl obsessed with outdoor power equipment! We are excited to share the knowledge and tips we have learned over our combined 55 years in the power equipment industry. We have both ran equipment dealerships and took pleasure in helping our customers everyday providing equipment repair, parts, purchasing, and business tips to our residential and commercial clients. We hope our blog will help you with your next purchase, repair, or project.

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