Does your lawn mower perform flawlessly when it’s cold, only to falter and stall when it gets hot? It can be incredibly frustrating, especially when we rely on our mowers during sunny days. As someone who has dealt with this issue personally, I’ve done extensive research to discover the causes and solutions. Let’s explore the most common culprits and find out how to get your lawn mower running smoothly again.
Table of Contents
The Spark Plug: A Common Culprit
One of the most likely reasons for a hot-starting problem is a faulty spark plug. If your lawn mower struggles to start or stalls when it’s hot, the spark plug is the first component to examine. Soot buildup, wear and tear, warping, or even cracked parts can render a spark plug ineffective.
To check if your spark plug is the culprit, turn off the lawn mower and inspect the plug. If you notice a burnt appearance or heavy soot/dirt accumulation, it’s time for a replacement. Although cleaning the spark plug is possible, it is advisable to replace it at least once a year. Ensure you select a spark plug that is compatible with your specific lawn mower model, as indicated in the manual. Getting an exact match is crucial.
Overheating Engine Issues
An overheated engine is another common cause of lawn mower stalling when it’s hot. The engine relies on cooling fins to dissipate heat and ensure continuous operation. However, grass clippings, dust, and dirt can accumulate around these fins, obstructing their function.
Instead of providing cooling, the clogged fins trap heat, causing the engine’s temperature to rise and eventually shut down. To resolve this problem, turn off the lawn mower, allow the engine to cool, and remove the casing. Use a brush or clean rag to clear away grass, dirt, and twigs from the cooling fins. Then, reassemble the casing and start the lawn mower. Regularly cleaning the cooling fins prevents dirt buildup and keeps your mower running smoothly.
Faulty Ignition Coil: A Possible Culprit
The ignition coil, also known as the flywheel magneto, produces the voltage required by spark plugs. If the engine overheats, the coil may struggle to generate sufficient voltage. However, old and worn-out coils can also become ineffective. To determine if your ignition coil is faulty, you can use a multimeter or an ignition coil tester such as the Ram Pro.
If you need to replace the ignition coil, consult your manual to find the exact type required for your lawn mower. Just like spark plugs, lawn mowers demand specific coils to function optimally.
Carburetor Complications
Carburetor issues directly affect the engine’s performance. Often, clogging caused by old gas deposits is the primary reason behind malfunctioning carburetors. Once gasoline has been sitting in the tank for over a month, it becomes gummy, obstructing proper carburetor function.
Cleaning the carburetor is typically the best solution. Acquire a carburetor cleaning kit and spray, such as the LImeiy Carburetors and STA-BIL Fast Fix. After cleaning, try starting the lawn mower again.
If cleaning fails to resolve the problem, physical damage to the carburetor might be the issue. In such cases, you have two options: repair the carburetor or purchase a new one. Generally, it’s recommended to replace the carburetor, as they are affordable and repairing them can be time-consuming.
Malfunctioning Valves
Compression problems caused by faulty valves can also lead to hot-starting difficulties. A simple test involves pulling the starter cord. If it pulls too easily, the valves are likely not functioning correctly, possibly due to an overheating engine or a broken valve itself.
Fixing or replacing valves requires experience with tools and DIY projects. Only proceed with this task if you are confident in your abilities. You can find a helpful instructional video on valve repair/replacement here.
Fuel Matters
Lawn mowers require the right type of fuel, preferably regular unleaded 87 octane E10. While premium gas can work, it won’t lead to significant improvements. However, even with the correct fuel, several issues can arise.
Old gas is a common problem. Replace the gas every 30 days, especially if you plan to store the mower. Draining the tank or using fuel stabilizer can prevent old gas from turning into sludge and clogging the engine.
Ensure you add the correct amount of fuel—neither too little nor too much. Too little gas prevents the engine from running, while an excess might flood it. Follow the manufacturer’s guidelines for the exact fuel quantity required for your lawn mower, and fill the tank only up to the designated line.
Be cautious when using different fuel types. Most lawn mowers are 4-stroke machines with separate oil and gas tanks. On the other hand, 2-stroke lawn mowers require a mixture of oil and gas. Never mix oil and gas in a 4-stroke lawn mower, as it can damage the engine.
Bolts and Screws: Stay Secure
Loose bolts and screws on a lawn mower can cause various problems. Replacing a part without securing the screws tightly or experiencing a jolt that loosens bolts are common scenarios. Loose bolts can lead to fuel leakage or air intake, negatively impacting the engine and eventually causing it to shut down. If the blade’s bolts loosen, the blade may detach from the mower.
To avoid potential hazards, regularly check and tighten screws and bolts on your lawn mower—especially if you have an older model. During maintenance, perform a thorough nuts and bolts inspection, tighten any loose ones, and replace any that are necessary. Pay particular attention to bolts on the engine and blades. Never operate a lawn mower with missing bolts; obtain replacements that are exact matches.
Worn Out Air Filters
Air filters in lawn mowers play a crucial role in shielding the carburetor from debris. Consequently, the filters accumulate dirt, debris, grass clippings, and dust. A clogged filter can spread trapped dirt throughout the engine, causing malfunctions.
Cleaning air filters is possible, but it’s often more effective to replace them. A general guideline is to replace filters after every 25 hours of use. Foam filters can be cleaned and reused, while paper filters are meant for one-time use.
If you choose to clean the filter, follow these steps: lift the filter housing cover off, remove the filter, and brush off any dirt. Wash the filter under running water if necessary, ensuring you avoid tearing it. While cleaning, inspect the filter for signs of tears or damage. If you notice any, it’s time to get a new filter.
Ensure a Clean Mower Deck
The mower deck prevents grass clippings and dirt from scattering, but it can become clogged over time. Excessive clogging prevents the blade from turning freely, forcing the engine to work harder and overheat.
To test if a clogged deck is the issue, attempt to pull the starter rope. If it requires more effort than usual or gets stuck, there’s a high possibility of excessive debris and clippings in the deck.
Turn off the lawn mower, allow the engine to cool, and flip the mower over to inspect the deck. You’ll likely find accumulated debris, grass, twigs, and other materials. Use a trowel or a similar tool to remove them.
By addressing these common issues, you can keep your lawn mower in optimal condition, ensuring it starts smoothly even when hot. Regular maintenance and attention to these potential culprits will help you avoid unnecessary frustration and costly repairs. Happy mowing!
