Common Lawn Mower Problems: Fixed!


There are many problems that are common to most lawn mowers on the market today. I have put together a list of issues that are most problematic over my years of working with lawn mower owners. Many of these items can be prevented with your annual mower maintenance.

The most common lawn mower problems are: 

  • Lawn mower won’t start
  • Lawn mower loses power & dies when mowing 
  • Lawn mower smokes 
  • Lawn mower won’t drive straight or steer right or left
  • Lawn mower won’t move

Most of these problems can be easily fixed by you. I’ll go over the common issues and explain how to fix them yourself or when you should bring your mower to a repair shop.

how to fix common lawn mower problems

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Lawn Mower Won’t Start 

A lawn mower may not start due to old fuel, dirty carburetor, bad fuel pump, dirty spark plug, dead battery, faulty safety switch or bad ignition switch.

No Gas in the Fuel Tank

I’m starting with the most obvious answer to the reason your lawn mower won’t start. Because the need for gas in your fuel tank is so obvious, it is often overlooked when diagnosing a starting problem.

FIX: Fill your gas tank with fresh gasoline that has an octane rating of 87 or greater and an ethanol content no greater than 10%. Find out more about the right type of gasoline for your mower here.

Bad Spark Plug

The spark plug can cause your lawn mower to not start. A plug that is excessively dirty, broken, or not gapped correctly can cause starting issues. If your mower started, but didn’t turn over, chances are the starting problem does not result from a bad spark plug. It had to have spark to try to start.

FIX: Remove the spark plug boots and the spark plugs. Check the plug for dark deposits or a cracked porcelain insulator. Replace the spark plug with a new spark plug if you find it to be bad. Reattach the spark plug boot to make sure you have a good connection. Ensure the spark plug is gapped correctly.

Bad Fuel Pump

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:

  • You must replace the fuel pump with a new fuel pump if you have notice any small cracks in the pump or if you notice fuel leaking from the housing.
  • 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

The carburetor is an essential part of your lawn mower. It allows the correct amount of air and fuel mix to enter the engine to create a combustion. When your carburetor gets gummed up and dirty from running old gas, it is not able to regulate this mixture which can cause your lawn mower to run rough or not start at all.

FIX: Most of the time, a dirty carburetor can be cleaned. If you are mechanically inclined you can use the instructions to clean your carburetor in this article. If you are not, you can replace the carburetor or bring to your local lawn mower repair shop to be cleaned.

Dead Battery or Loose Connections

A battery that is dead, won’t hold a charge, has corroded terminals or connections can cause your lawn mower not to start. 

FIX: Make sure your battery connections are securely in place and inspect your battery terminals for corrosion. If your battery terminals are corroded, clean them using a baking soda scrub (2 cups of water & 3 rounded tablespoons of baking soda) and a wire brush. Replace the terminals if you are not able to get them clean.

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

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. It may also not start if you don’t follow the correct starting procedures. A bad safety switch can cause your lawn mower not to start.

FIX:  Temporarily bypass the safety switch to identify a bad switch and replace with a new switch. Warning: Do not operate a mower without the safety switch installed for your safety. People get injured due to not having their safety features installed. Don’t play the odds and hope you are one of those lawn mower owners that won’t have an incident so safety switches are not needed.

Broken Recoil on a Push Mower

Many push mowers use a recoil to start the mower. A bad pulley or spring in your lawn mower can cause the mower to not start. On some occasions, it is easy to restring your recoil and replace a spring. Other times, it is easier to replace a broken recoil.

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.

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 is not able to fire.   

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

Faulty Charging System  

The charging system charges the battery while your mower is running. If the charging system doesn’t work, your battery will eventually die. I show steps on how to test your charging system using an ohm meter.  

FIX: If you find the problem is in your charging system, have a small engine mechanic identify what is the actual cause of the failure. It could be several different items. Throwing different parts at your lawn mower to fix the charging issue can get pretty expensive when you are trying to isolate the problem.

Lawn Mower 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. 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 the 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

Your lawn mower 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. 

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 shields are 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: Use clamps to stop and release the flow of fuel to check for clogs in the fuel lines. Once a clog is found, remove the fuel line and spray carb cleaner in the line to loosen the clog. Finish removing the clog with compressed air. If you don’t have an air compressor, you can use a can of compressed air found at hardware and office supply stores.

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: 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.  

Lawn Mower 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 

Most people know that you need can’t let your engine oil level get too low, but not many know you can run into problems when you put too much oil in your engine. Too much oil in the crankcase can cause pressure to build which can allow oil to get into the cylinder and into the air intake through the valve train.

As the oil in the cylinder gets hot and burns off, it 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 out of the crankcase and then retighten. 
  • Vacuum some oil out of the engine through the oil fill hole using an evacuator.
  • Use a turkey baster to suck a little oil out of the oil fill tube. 
  • Unscrew the filter and use a rage 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: You can try to add fresh oil to your engine and see if it will run, but most of the time, engine damage has already happened. Bring your mower to a small engine mechanic so the mechanic can assess the damage to determine whether the engine can be repaired or needs to be replaced.

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

Remove your spark plug and check for oil on the plug. This is an indication you have an internal engine problem. Excessive oil on the spark plug indicates a possibles piston 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 if it makes financial sense to invest in a new push mower.

Weak Hydrostatic Transmission 

This section applies to mower that use a hydrostatic transmission. There are simple things to check to make sure your hydrostatic transmission performs well and keeps your lawn mower 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 your hydro pump leaking oil or your mower moves when it is warm, but fails to move when it is cold.

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 lawn mower 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. 

Mower Won’t Drive Straight or Won’t Turn Left or Right

It’s frustrating to always have to compensate for your lawn mower pulling a little to the left or a little to the right or your mower just won’t turn left or right when you move the steering wheel. There are some simple adjustments you can make to correct your mower’s steering problem.

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 with the psi level recommended in your owner’s manual.

Bad Dampners on Zero Turn

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 on Zero Turn 

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.  

Worn or Loose Steering Components on a Riding Mower

When you turn your steering wheel on your riding mower, the mower may not turn right or left.  This may be due to worn or loose washer, bushings or gears.

FIX: There is a washer at the base of the steering shaft on many riding mowers. Tighten the washer as it can come loose over time. You may have bushings in the steering shaft that are wearing that can result in your steering problem. If neither of these items are your problem, check the gears near the base of the steering shaft to ensure they are functioning properly and there isn’t any slippage of the gears.

Lawn Mower Won’t Move

There are many reasons why a hydrostatic lawn mower will not move. I have listed below the reason why your lawn mower may not move, but you can read more about these reason in my article, “9 Reasons Your Mower Won’t Move or Go Forward”.

  • Drive release lever is not in operating position: The drive release lever exists so you can release the hydro system so you can free roll the mower if needed.
  • Missing key in the axle: Many riding mowers have a key in the axle that can fall out when changing the wheel.
  • Drive or pump belt is worn: Replace a belt that is worn or cracked. Make sure it is sitting on the pulleys as designed.
  • Bad tensioner pulley: The bearing in the pulley can fail.
  • Missing idler arm spring: The spring keeps tension on the drive belt.
  • Low hydraulic level or hot hydraulic.
  • Air in the hydraulic system

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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