A push lawn mower not starting can be very frustrating, especially when you need to get the lawn mowed. There are several common reasons a push mower may fail to start, but the good news is that many issues can be fixed with some basic troubleshooting and maintenance. In this article, we’ll go through the top causes of push mowers not starting and provide tips to get your mower running again.
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Fuel Related Issues
Fuel issues are one of the most common reasons a push mower won’t start. Here are some of the specific fuel-related problems that can occur:
Empty Fuel Tank
This one may seem obvious, but it’s easy to overlook an empty fuel tank as the culprit. Check the fuel level in the mower’s tank before doing anything else. If the tank is bone dry, refill it with fresh gasoline. Make sure to use the type of fuel recommended by your mower’s manufacturer.
Old or Bad Gasoline
Gasoline can go bad over time, causing issues like varnish build-up in the carburetor and fuel lines. Old gas loses volatility, making it harder for the engine to ignite the fuel. The shelf life for gasoline is generally 3-6 months when stored properly in an airtight container. If you suspect bad gasoline, drain the old fuel completely and replace with fresh fuel.
Dirty Carburetor
The carburetor is responsible for mixing air and fuel in the right amounts to power the engine. Over time, gum, varnish and dirt can build up inside the carburetor, clogging its tiny fuel passages. This restricts fuel flow, preventing the engine from getting the fuel it needs to run.
Cleaning the carburetor with carburetor cleaner can often resolve this issue. In some cases, the carburetor may need to be rebuilt or replaced altogether.
Clogged Fuel Filter
The fuel filter screens out contaminants from the fuel supply on its way to the carburetor. When the filter gets clogged with debris, it can block fuel flow to the engine. Check your mower’s fuel filter and replace it if it looks dirty.
Engine Oil Issues
Engine oil problems are another prime suspect when troubleshooting a push mower that won’t start. Here’s how oil can cause problems:
Low Oil Level
All mowers require oil in the crankcase to lubricate internal components. If the oil level falls below the minimum, it can prevent the engine from starting as a failsafe to protect it from damage. Check the dipstick and add oil if needed. Refer to your owner’s manual for details on oil type and capacity.
Thick, Sludgy Oil
Extremely thick, gunky oil can have the same impact as low oil, coating and starving vital components that need lubrication to operate. Change the oil if it looks like molasses. Be diligent about regular oil changes to prevent excessive thickening over time.
Ignition System Problems
Issues in the ignition system can prevent the spark needed to ignite the fuel-air mixture. Here are some common ignition problems:
Faulty Spark Plug
Spark plugs provide the spark for combustion. Over time, spark plugs can become fouled or damaged, resulting in weak or no spark. Inspect the spark plug. If it’s fouled, try cleaning it. Otherwise replace it with a new plug of the same type. Ensure the replacement gap is set correctly.
Spark Plug Boot Damage
The spark plug boot connects the spark plug to the ignition wiring. Cracked or damaged spark plug boots interrupt the spark. Check this component and replace the boot if needed.
Faulty Magneto
The magneto generates voltage for the spark plug. If the magneto is defective, there will be no spark. A damaged magneto usually requires replacement by a small engine repair technician.
Compression Problems
Lack of engine compression makes it difficult for the fuel to ignite. Some compression-related causes include:
Blown Head Gasket
The head gasket seals the gap between the engine block and cylinder head. A blown gasket causes loss of compression. Replacing the head gasket is needed to restore compression.
Stuck or Sticky Valves
Valves control air-fuel flow in the cylinder. Stuck valves don’t seal properly, reducing compression. Sticky valves open sluggishly, also causing low compression. Valves may require repairs by a technician.
Worn Piston Rings
The piston rings seal the combustion chamber to maintain good compression. Badly worn rings allow pressure to leak past the piston, robbing compression. The only solution is to overhaul the engine and install new rings.
Safety Interlock Issues
Safety features that prevent accidental starting can sometimes malfunction and prevent starting.
Faulty Blade Brake/Clutch
Most mowers have a blade brake or clutch that disengages the blade when the bail handle is released. If this sticks, it activates the safety interlock. Try lubricating and freeing up the blade brake/clutch mechanism.
Defective Safety Key
The safety key fits under the blade control handle and grounds the ignition system when engaged. A faulty safety key interrupts the ignition, preventing starting. Replace the safety key if faulty.
Problem with Safety Switch
Many mowers have a safety switch tied to the blade control that grounds the ignition when the control is released. Issues with the switch or wiring can prevent starting. Test and repair or replace as needed.
Mechanical Issues
Mechanical problems in the engine can make it impossible to start the mower:
Seized Engine
If an engine seized from lack of oil, trying to force it to start will only cause more damage. A seized engine needs to be repaired or replaced.
Thrown Rod
A thrown rod is when a connecting rod breaks free and damages the crankshaft and cylinder walls. The extensive engine damage means the mower will not start until the engine is rebuilt or replaced.
Bent Crankshaft
Hitting an object can bend the crankshaft just enough to prevent the engine from turning over. A bent crank requires repairs by a technician to get back in shape.
Electrical System Problems
While push mower engines themselves don’t rely on electronics, some supporting systems involve electrical components that could cause no start issues:
Dead Battery (Electric Start Models)
Some self-propelled mowers have electric start requiring a battery to operate the starter. A dead battery prevents electric start, though the mower can still be started manually with the recoil starter in most cases. Recharge or replace the battery.
Faulty Solenoid (Electric Start Models)
The starter solenoid is an electromechanical component that engages the starter when energized. A bad solenoid won’t activate the starter motor. Test and replace the solenoid if it’s defective.
Damaged Starter Motor (Electric Start Models)
Again affecting only electric start models, a damaged starter motor itself can prevent the engine from cranking over. Have the starter inspected and repaired or replaced as needed.
Conclusion
While this covers the most common issues, every situation is unique, so further troubleshooting may be needed. The key is methodically isolating the potential causes. Go through each fuel, ignition, compression and mechanical system one-by-one until finding the problem. Test components and make repairs or replacements as required. Use the maintenance schedule in your mower’s manual to prevent future issues. With some diligent detective work and a little luck, you’ll be ready to mow again in no time!