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 has a weak hydrostatic transmission
- Lawn mower won’t drive straight or steer right or left
- Lawn mower won’t move
- Lawn mower is cutting uneven
- Lawn mower is leaking gas
Most of these problems can be easily fixed by you. I’ll go over the common issues and explain the solutions so you can determine whether you want to tackle the task or not.
Always follow safety guidelines outlined in your mower’s operator’s manual to prevent injury while working on your lawn mower.
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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.
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.
Detailed information can be found at:
Lawn Mower Won’t Start: Solved!
| Cause | Reason for Problem | Solution |
| No gas in the fuel tank | Fuel tank is empty | Fill with fresh fuel |
| Bad or old fuel | Fuel breaks down overtime making your fuel less efficient and prone to clogging the fuel system | Drain the fuel tank and fill it with fresh fuel. Use a fuel additive like Sea Foam to stabilize the fuel and assist with cleaning the fuel system. Use the right fuel. |
| Faulty or clogged fuel cap | The vent in the cap can get clogged causing your tank to form a vacuum restricting fuel flow | Use a thin piece of wire to try to clear the clogged vent. Replace the cap if needed. |
| Bad spark plug | Excessively dirty or broken spark plug; bad connection; not gapped correctly | Replace with a new spark plug, secure connections, and ensure it is gapped to manufacturer specifications |
| Plugged air filter | Dirt and grass can plug the air filter preventing airflow | Remove the filter and clean it. Replace the filter if it is in bad condition. |
| Plugged fuel filter | A dirty fuel filter will restrict fuel flow | Replace the fuel filter |
| Bad fuel pump | A failed or leaking fuel pump will no longer create the pressure needed to pump fuel | Replace the fuel pump |
| Blocked fuel lines | Bad fuel deposits and dirt can build up and clog the fuel lines preventing the engine from getting the required fuel | Use a carb cleaner and compressed air to clear the clog out of the fuel line. Replace the lline if necessary. |
| Dirty carburetor | The carburetor can become dirty and clogged due to bad fuel and ethanol deposits preventing fuel flow | Clean the components making up the carburetor. Replace if needed. |
| Bad battery or loose & dirty terminals | A dead battery, loose cables, or corroded terminals can cause starting problems | Charge your battery and replace it if it won’t hold a charge. Make sure your cables are tight and clean the corrosion from terminals. |
| Bad safety switch | Safety switches are a safety measure that exists to prevent your mower from starting in certain situations. When a switch fails, your mower may not start. | Test and replace faulty safety switch |
| Bad ignition switch or coil | Your mower will not start when either the ignition switch or coil is bad | Test and replace a bad switch |
| Broken recoil | A pull start mower may have a damaged or broken recoil preventing the recoil to initiate starting your engine | Check the recoil to see if it can be restrung or broken parts, like the pulley, can be replaced. Replace the recoil assembly if needed. |
| Bad Starter Solenoid | An ignition switch that hums when turning the key indicates you may have a problem with the starter solenoid causing a starting problem. | Test the starter solenoid and replace if bad. |
Lawn Mower Loses Power and Dies While Mowing
Your lawn mower may die while mowing when your fuel system or air filtration system is clogged. This could be from a plugged air filter, a dirty carburetor, or bad fuel. You’ll also want to take a look at everything that may be failing to keep your engine cool like dirt and grass packed around the engine or broke cooling fins.
Detailed information can be found at:
Your Lawn Mower Dies While Mowing
| Cause | Reason for Problem | Solution |
| Bad fuel | Fuel breaks down overtime making your fuel less efficient and prone to clogging the fuel system and engine damage. | Drain the fuel tank and fill it with fresh fuel. Use a fuel additive like Sea Foam to stabilize the fuel and assist with cleaning the fuel system |
| Plugged air filter | Dirt and grass can plug the air filter preventing airflow. | Remove the filter and clean it. Replace the filter if it is in bad condition. |
| Dirty or broken cooling fins | Cooling fins get packed with dirt, oil, and grass not allowing air to effectively cool the engine block. | Replace broken fins and clean the cooling fins. |
| Clogged fuel lines | Bad fuel deposits and dirt can build up and clog the fuel lines preventing the engine from getting the required fuel. | Use a carb cleaner and compressed air to clear the clog out of the fuel line. |
| Dirty carburetor | The carburetor can become dirty and clogged due to bad fuel and ethanol deposits preventing fuel flow. | Clean all of the components making up the carburetor. Replace if needed. |
Lawn Mower is Smoking
Some of the same reasons mentioned above for your lawn mower shutting down while mowing can be found in the reasons your lawn mower is smoking as well. Smoke can develop when your engine is running too rich and you’re burning more fuel than air.
Another reason you may notice smoke is when engine oil is burning off due to an oil leak, insufficient oil level, or an internal engine problem.
Detailed information can be found at:
Why Your Lawn Mower is Smoking
| Cause | Reason for Problem | Solution |
| Plugged air filter | Dirt and grass can plug the air filter preventing airflow. | Remove the filter and clean it. Replace the filter if it is in bad condition. |
| Too much oil in the crankcase | Excessive oil can cause pressure to build in the engine allowing oil to get into the cylinder through the valve train. | Drain a little engine oil until it is at the manufacturer’s recommended oil level. |
| Engine oil level is too low | Lack of oil can increase friction in your engine causing extreme heat. | Bring to a small engine repair shop to inspect engine damage. You can try adding oil, but it is often too late to this fix your engine problem. |
| Internal problems including the piston ring, valve train or engine gasket | Internal engine problems can have a detrimental effect on your mower if they are not caught soon enough and fixed. | Bring your lawn mower to your local small engine repair shop for troubleshooting. |
Weak Hydrostatic Transmission on a Lawn Mower
A lawn mower with a hydrostatic transmission may experience a weak transmission when the hydraulic oil is low or old. A bad hydro belt or pulley can also make your transmission seem like it weak.
Note: Some transmissions are non-serviceable. This means you are unable to change the hydraulic oil because the system is sealed. Bring your mower to your local lawn mower repair shop when you have problems with your hydraulic system.
| Cause | Reason for Problem | Solution |
| Bad drive belt | A bad drive belt can cause your pump not to work efficiently. | Replace a frayed, cracked, or worn belt. |
| Bad tensioner pulley | When a tensioner pulley fails, it fails to keep tension on the drive belt. | Replace the pulley and grease the tensioner arm. |
| Low or old hydraulic oil | Low or old hydraulic oil can fail to lubricate the hydraulic system causing your hydraulic system to seem weak. | Change your hydraulic oil at regular intervals as recommended by the manufacturer. Check your hydraulic oil periodically to ensure your hydraulic fluid is full. |
Lawn 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.
| Cause | Reason for Problem | Solution |
| Incorrect tire pressure | Unequal tire pressure can cause your mower to pull to one side. | Check tire pressures and keep them filled to the manufacturer’s spec. Tires on each side of your mower require equal pressure. |
| Bad dampers on zero turn | Bad dampers will cause your mower to jerk to one side when moving forward. | Replace with a new damper. |
| Tracking adjustment needed on zero turn | When one tire is moving faster than the other, your mower can pull to one side. | Adjust the speed adjustment bolt to change the rotation speed of the tire. Refer to your owner’s manual. |
| Worn or loose steering components in riding mower | Worn bushings, washers, and gears can cause your mower to not steer one way or the other. | Inspect and replace the parts that failed on your steering system. |
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, including old hydraulic oil or a low oil level.
Hydrostatic transmissions are used in most current riding mowers and zero-turn mowers, however, there are different procedures and steps to servicing each type. Refer to your owner’s manual for details on caring for your hydraulic system.
Detailed information can be found at:
9 Reasons Your Mower Won’t Move or Go Forward
| Cause | Reason for Problem | Solution |
| Drive release lever in the wrong position | The drive release lever allows hydrostatic mowers to roll freely. | The drive release lever must be in the operating position. |
| Missing key in the axle | Your riding mower may have a small key in the axle that may have fallen out of place. | Replace the key in the axle. |
| Drive pump belt is worn | The mower won’t move if your drive belt has fallen off. It could also not move if the belt is worn. | Replace a worn or cracked belt. Make sure the belt is securely around the pulleys. |
| Bad tensioner pulley | The bearing in the tensioner pulley can fail. | Replace the tensioner pulley. |
| Missing idler arm spring | If the idler arm spring breaks or goes missing, it can no longer place tension on the drive belt. | Replace the broken or missing spring. |
| Low or old hydraulic oil | Low or old hydraulic oil can fail to lubricate the hydraulic system causing your hydraulic system to seem weak. | Change your hydraulic oil at regular intervals as recommended by the manufacturer. Check your hydraulic oil periodically to ensure your hydraulic fluid is full. |
| Hot hydraulic fluid | Hot hydraulic fluid can be a sign of damage to your hydrostatic transmission system. | Let your hydraulic oil cool. If you find your mower runs fine when it is cold, but becomes weak when the hydraulic system gets hot, have your mower checked at your local lawn mower dealership. |
| Air in the hydraulic system | Air must be bled from the hydraulic system after changing your hydraulic fluid or the mower will not be able to move at normal speeds. | Follow the manufacturer’s procedures for changing the hydraulic fluid and bleeding air from the system in your owner’s manual. |
Lawn Mower is Vibrating
There are many reasons a lawn mower may start to vibrate. You could have some missing or broken parts or it could be from debris that is stuck in the mower. It’s important to look your mower over closely as the littlest items can cause a big vibration.
Detailed information can be found at:
How to Stop Your Lawn Mower from Shaking & Vibration
| Cause | Reason for Problem | Solution |
| Loose or missing engine mounting bolts | Engine bolts are used to reduce the vibration of the mower when the engine is running. | Secure engine bolts and replace any missing bolts. |
| Clutch is bad | When there is bearing failure and it falls out of the clutch it can cause vibration. A manual engagement clutch can have a bushing and linkages that can fail. | Replace the clutch. |
| Unbalanced or damaged mower blades | Damaged and unbalanced blades can send a vibration through your mower. Blades must be balanced before installing. | Replace any damaged blades and make sure they are balanced. |
| Material wrapped around the blade spindle | Foreign materials like string or long weeds can get wrapped around your blade shaft causing vibration. | Remove all debris and items wrapped around the blade shaft. Check for spindle damage. |
| Bad spindle housing bearings | Vibration can be caused by a bad bearing in the spindle housing. | Replace the bearing in the spindle housing or replace the whole spindle housing assembly. |
| Worn pulleys or deck belt | Check deck belt and pulleys for wearing of the belt and bearing failure in the pulleys. | Replace any damaged or worn belts and pulleys. |
| Debris lodged in mower | The smallest little things can cause your lawn mower to excessively vibrate. Check over your mower for debris stuck in the deck or mower. Don’t overlook the small stuff. | Check over your mower deck and mower for any place small items can be stuck in your mower. Remove these foreign materials. |
Lawn Mower Has a Bad or Uneven Cut
An uneven cut with your lawn mower doesn’t always indicate a problem in the mower deck. It can be something as simple as a low tire that can make you’re your mower not sit level. Always check the tire pressure first and then move on to looking at your mower deck.
Detailed information can be found at:
Reasons a Lawn Mower Cuts Uneven
| Worn mower blade | Uneven tire pressures | Engine speed is too low |
| Bent mower blade | Unleveled mower deck | Ground speed is too fast |
| Blade installed wrong | Bent blade spindle or spindle bearing | Damaged deck shell |
| Clogged Mower Deck | Worn deck pulleys or belt | Operator error |
Lawn Mower is Leaking Gas
It can be difficult to find fuel leaks in your lawn mower because fuel evaporates into the air. By the time you realize you have a leak, there may not be a large wet spot giving you a clue to the area of the leak. Your only clue may be the strong odor left in your garage.
When looking for a fuel leak, follow your fuel lines starting at the fuel tank. Check every component that makes up your fuel system for leaks.
Detailed information can be found at:
This is Where a Lawn Mower is Leaking Gas
| Cause | Reason for Problem | Solution |
|---|---|---|
| Dirty of Failed Carburetor | The carburetor can collect a buildup of substances remaining from old gas that can cause blockages or parts failures. | Clean the carburetor and replace any damaged parts. |
| Old Fuel Filter | An old fuel filter can degrade and the plastic seams can begin leaking. | Replace fuel filter. |
| Bad Fuel Pump | Pump can wear and deteriorate over time and may begin leaking at the seams. | Replace the fuel pump. |
| Bad Fuel Tank | A metal tank can develop a rust hole. A poly tank can leak at the seams of the tank. | Replace the fuel tank. Sometimes, a rust hole can be repaired if you can no longer find a replacement tank. |
| Bad Fuel Shut-Off Valve | Metal and plastic shut-off valves are prone to leaking. | Replace the shut-off valve. |
| Cracked Fuel Lines | Rubber fuel lines become dry and cracked causing gas to leak. | Replace the fuel lines. |
| Cracked Primer Bulb | The rubber of the primer bulb can begin leaking when it cracks or isn’t attached well to the fuel hose. | Replace the primer bulb. |
| Bad Seal in the Gas Cap | The gas cap seal can fail and no longer seal allowing gas to splash out of the fuel tank around the gas cap. | Replace the gas cap. |