Your Guide to Common Lawn Mower Problems
and How to Fix Them
Spring is here, which means it's time to dust off your lawnmower and put on your dad shoes! As the days grow longer, so does the grass in your yard. Among all the tools for maintaining a pristine lawn, the lawnmower is the most essential. However, like any machinery, it can cause problems, especially after sitting in the shed over the winter.
Before taking your mower to the shop, it's worth trying to diagnose the issue yourself first. Learning how to troubleshoot common problems can save you both time and money. While it's not as easy as simply turning a computer off and on, you'll gain a better understanding of how your lawnmower operates and any quirks it might have.
At SteveCo Power, we appreciate the smooth hum of lawn mower engines. We understand that not every problem requires a trip to the shop. That's why we've created this guide to help you troubleshoot and resolve most minor issues on small walk-behind mowers, so you can quickly return to mowing. If you still encounter difficulties after trying our troubleshooting tips, our expert technicians are available to help you get your machine up and running again.
Are you ready? Let's get started!
How to Flip the Lawn Mower On Its Side
Most maintenance tasks for your small walk-behind lawnmower, such as adding gas or changing the air filter, can be performed while the mower is upright. However, some tasks require you to flip the mower on its side, such as removing the blade and cleaning the underside of the deck. If you flip it over incorrectly, it can cause fuel to leak out of the carburetor or into the cylinder and crankcase, or it could cause oil to leak into the carburetor. The best method is to tip the mower straight backwards so that the engine oil pools at the back of the engine. This position prevents the engine oil from coming into contact with the carburetor, muffler, valves, cylinder, sparkplug, or engine breather.
If you have already flipped the mower the wrong way and it won't start, you may need to take it to a repair shop for assistance.
The Lawn Mower Won’t Start
One of the most common and frustrating problems is when your lawnmower refuses to start. Here are some typical causes and solutions:
Check the Fuel
- Empty Tank: It might sound obvious, but it happens to everyone at some point. Make sure your fuel tank isn't empty. You may have drained it and forgotten about it. If it is empty, fill it up with fresh gasoline.
- Stale Fuel: Old fuel loses its flammability, which can prevent the engine from starting and may cause more significant issues, such as gumming up the carburetor. If the gas has been sitting for more than a few months, drain the tank and the carburetor, then add fresh fuel. If the engine still doesn't start, the carburetor likely needs to be removed and cleaned, which should be done by a repair shop. To avoid dealing with stale gas in the future, drain the tank at the end of the mowing season and run the engine until it is completely out of fuel. However, the problem usually occurs in the carburetor rather than the tank. As a best practice, at the end of the season, add a fuel stabilizer, and start and run the engine every few weeks to circulate the gas through the carburetor.
Inspect the Air Filter
- Clogged Air Filter: A clogged air filter can hinder your mower's performance, resulting in reduced power and eventually preventing it from starting at all. A clogged air filter restricts airflow, affecting the engine's fuel-to-air ratio, and causes the engine to run rich, which can eventually lead to a fouled spark plug. The filter can get clogged with dirt over time or with gasoline if the mower was tipped over improperly. Replace the air filter if possible, but if not, try cleaning it with the intention of replacing it as soon as possible.
Inspect the Sparkplug
- Fouled Sparkplug: When the sparkplug becomes fouled, it can prevent a lawnmower from starting by failing to transfer the necessary spark to ignite the fuel-air mixture in the engine's combustion chamber. Remove the sparkplug and inspect it for any dirt or damage. If you don't have a new sparkplug available, you can try cleaning it with a wire brush, but it's always best to replace it if necessary.
- Loose Connection: Ensure the sparkplug is properly connected to the ignition coil wire. A loose connection can cause intermittent spark, leading to engine misfires.
Check the Spark
- Defective Ignition Coil: A defective ignition coil usually requires a shop to diagnose it, unless you have an inline spark tester. If you have the right tools, check the engine for proper spark. If the spark is weak or non-existent, the ignition coil is likely the culprit.
Inspect the Flywheel Key:
- Sheared Flywheel Key: A sheared flywheel key can prevent the engine from starting. This problem typically occurs from hitting a solid object while mowing. A sheared flywheel throws off the engine timing, causing it to misfire. It's best to receive professional help from a shop for this problem, but if you want to try it yourself, first remove the top shroud and the flywheel, and inspect the flywheel and keyway for any visible damage. If the key is sheared, it will appear broken or out of alignment. In such cases, it will need to be replaced.
Engine Lacks Power
If your mower starts but runs rough and lacks power, it could be due to several reasons:
Fuel System Issues
A full tank of the freshest fuel you can find won't help if your mower can't get the gas from the tank to the combustion chamber. Potential symptoms of a defective fuel system are:
- Dirty Carburetor: A dirty carburetor can disrupt fuel flow. This usually requires the carburetor to be removed and disassembled for cleaning. It can be a tedious task, with numerous small parts and gaskets, so if you're not familiar with the inner workings of a carburetor, it's best to have it done by a professional shop.
- Clogged Fuel Tank Vent: The fuel tank needs to breathe; if air can't get into the fuel tank, gas can't flow out of the tank. On small mowers, this is typically achieved through a check valve in the fuel cap. Remove the fuel line from the carburetor and inspect the fuel flow. If the fuel is only trickling out at a slow pace, remove the fuel cap. If the fuel flow increases, the fuel tank vent is likely clogged. If there are no visible external vents on the tank, replace the fuel cap.
- Clogged Fuel Line: Remove the fuel line from the carburetor and inspect the fuel flow. If the fuel is only trickling out at a small pace, you have a fuel delivery issue. As mentioned previously, remove the fuel cap. If the fuel flow doesn't increase, inspect the fuel line for blockages and clean it if necessary.
Air Filter Problems
- Dirty Air Filter: Similar to starting issues, a clogged air filter restricts airflow, affecting the engine's fuel-to-air ratio, and causes the engine to run rich, causing it to run rough and resulting in black smoke and reduced power. Over time, debris such as dust, dirt, and other airborne particles, including pollen, will accumulate on the filter, reducing airflow and affecting performance. Ensure it's clean and replace it if necessary.
Spark Plug Problems
- Loose Ignition Coil Wire: Ensure the sparkplug is properly connected to the ignition coil wire. As mentioned before, a loose connection at the sparkplug can cause intermittent spark, leading to engine misfires.
- Cracked Sparkplug Boot: Another common issue with the ignition system is that the sparkplug boot cracks or breaks. Be aware that some cracks are nearly invisible and difficult to detect unless you know exactly what you're looking for. A cracked sparkplug boot allows the spark to escape through the crack and ground out against the shroud or a metal component of the engine, causing the engine to misfire.
- Worn or Damaged Spark Plug: A faulty spark plug can cause the engine to misfire. Some sparkplug problems are undetectable, and the sparkplug may still appear to be in good condition. If none of the previous issues are present and you have a spare sparkplug available, it may be worth replacing the original sparkplug, just to see if the problem persists.
Timing Problems
- Sheared Flywheel Key: A sheared flywheel key often causes the engine to run poorly or not at all. As mentioned earlier, it's best to receive professional help from a shop for this problem. However, if you want to try it yourself, first remove the top shroud and the flywheel, and inspect the flywheel and keyway for any visible damage. If the key is sheared, it will appear broken or out of alignment. In such cases, it will need to be replaced.
Uneven Grass Cutting
An uneven cut can ruin the appearance of your lawn. A good mower blade makes a nice, clean cut. If your mower is cutting unevenly, here are a few things to check:
Blade Maintenance
- Dull Blades: Dull blades tear grass instead of cutting it cleanly, resulting in the tips of your grass blades turning dull white or brown, and exposing your lawn to disease and weeds, which can eventually cause your grass to die prematurely. Sharpen the blades regularly to prevent this.
- Unbalanced Blades: When sharpening the blade, it's crucial to ensure it is properly balanced, especially on small walk-behind mowers, since the blade is mounted directly to the engine. This requires a balancing tool specifically designed for lawn mower blades. While an unbalanced blade typically doesn't affect cutting performance, it can cause excessive vibration and lead to premature wear on the engine or mower.
- Bent Blades: Hitting rocks or lawn edging will damage your blades or even bend them. This will inevitably cause an uneven cut. Replace them if they are even slightly bent or damaged beyond repair.
Deck Maintenance
- Uneven Cutting Deck: The most common cause of an uneven cut in your lawn is an unlevel cutting deck. To determine if your mower deck is not level, first disconnect the spark plug wire for safety. Then, place the mower on a flat surface with the blade oriented from side to side. Measure the distance from the ground to the furthest tip of the blade on both sides. If the measurements differ by more than 1/8 of an inch, inspect the blade to ensure it isn't bent. If the blade is fine, you may need to adjust the mower deck. The process for adjusting your mower deck varies depending on the model, but it is generally straightforward. If you are unsure how to proceed, consider contacting your local repair shop for assistance. Other potential reasons for an uneven cutting deck include worn-out bushings, bearings, or wheels.
- Clogged Cutting Deck: The mower deck relies on the airflow generated by the blades to cut grass effectively. If the cutting deck becomes clogged, it can restrict airflow, resulting in missed patches, clumps of grass, and an uneven cut. It's essential to regularly clean the underside of the mower deck to remove any debris or grass clippings that may have accumulated.
Smoke Coming Out of the Engine
Seeing smoke from your mower can be alarming. But, like the papal conclave, different smoke colors have different meanings. Here are the most common culprits of a smoking engine.
- Blue or White Smoke - Oil Issues: Blue or white smoke typically results from the engine burning off excessive oil. Check the oil level, and if it's overfilled, inspect the oil closely for a fuel-like smell. A defective carburetor can cause fuel to flood through the carburetor into the engine's crankcase, creating the appearance of an overfilled oil level. Additionally, gas in the oil can result from improperly tipping the mower onto its side. If the engine is smoking white or blue, and the oil level is not overfilled, the cause is likely a blown head gasket, a worn or damaged cylinder wall, or worn piston rings. A detailed evaluation by a repair shop is required to determine the condition of the internal components.
- Black Smoke - Rich Fuel Mixture: Black smoke indicates a rich fuel mixture, usually caused by a clogged or dirty air filter or a faulty carburetor. A clogged air filter restricts airflow, disrupting the fuel-to-air ratio. Inspect and replace the air filter if it's dirty. If the problem persists, the problem may be with the carburetor, particularly with the auto-choke. Most engines on small walk-behind mowers feature an automatic choke, which makes it easier to start the engine. If the auto-choke is malfunctioning, it can cause the engine to run rich. Because carburetor repair can be complex and varies by model, consider taking the mower to a local repair shop if replacing the air filter doesn't fix the problem.
Proper Maintenance Procedures
Maintenance is often easy to overlook, especially if you don't use your mower frequently. However, it is essential for extending the lifespan of your mower. Below are key factors to check before the mowing season begins, as well as throughout the season:
Engine Maintenance
- Air Filter: Air filters play a crucial role in removing dirt, dust, and debris from the air before it enters the engine, primarily to protect the engine cylinder. When an air filter becomes clogged, it can restrict airflow, leading to power loss and the accumulation of carbon on components such as the spark plug, cylinder head, and piston. To maintain optimal engine performance, it's important to clean or replace the air filter regularly.
- Fuel Filter: The purpose of a fuel filter is to clean the fuel before it reaches the carburetor. Contaminated fuel can clog the carburetor, potentially preventing the engine from starting or running smoothly. While not all mowers come with a replaceable inline fuel filter, if applicable, it's important to inspect the fuel filter regularly and replace it when necessary.
- Sparkplug: The condition of the sparkplug greatly depends on the condition of the air filter. Keeping the air filter clean helps maintain the sparkplug, but it should still be inspected annually and replaced if it's severely discolored.
- Stale or Contaminated Fuel: A fuel filter cannot protect the carburetor and engine from poor-quality fuel. Always use fresh, high-quality fuel, typically with an octane rating of 87. Regularly add fuel stabilizer to your fuel, especially at the end of the season. While draining the fuel tank at the end of the season is common practice, fuel issues often occur in the carburetor. If you drain the fuel tank, you should also drain the carburetor. Even after draining, fuel residue is typically still present and can cause the o-rings and gaskets to dry out and crack. It is best practice to keep a small amount of treated fuel in the system and to run the mower for a few minutes every few weeks to circulate the fuel through the carburetor and the fuel system.
Mower Maintenance
- Sharpen and Balance the Blade: Keeping the blade sharp and properly balanced is essential not only for achieving peak performance from your mower but also for the health of your lawn. Regularly inspect the blade, and if it becomes damaged or dull, sharpen it, ensuring it is properly balanced as well.
- Clean the Mower Deck: Maintaining a clean cutting deck is just as crucial for your mower's performance. Regularly clean the underside of the deck to remove any obstructions and ensure optimal airflow and cutting performance.
Conclusion
While DIY fixes can be effective, some problems need professional help. If you are unable to resolve an issue or are uncertain about making repairs yourself, we are here to help!
At SteveCo Power, we are the premier provider of outdoor power equipment sales and service in Lancaster, PA. Our expert technicians have the knowledge and tools to quickly diagnose and resolve any issue, ensuring your mower runs smoothly and efficiently. And if you need to mow while we're repairing your mower, you can rent one from us, so your mowing schedule won't be disrupted.
With 35 years of experience, we're here to help keep your lawn mower running at its best, whether it's a simple fix or a more complex repair.
Contact us today to discover how we can help you achieve the perfect lawn!
Common mower problems can be so frustrating when you’re on a tight schedule. The guide’s breakdown of issues—like air filter clogs and dull blades—matched exactly what I experienced last fall. It’s good to know which fixes I can do myself versus calling a pro. What’s the most overlooked maintenance step that causes issues?