Lawn mower is hard to start: Common Causes & How to Fix
1Lawn Mower Spark Plug
Most Common Solution
Repair Instructions:
Check the lawnmower's spark plug for any wear or damage. If you see a cracked porcelain insulator, a burnt or damaged electrode, or excessive carbon buildup on the electrode, it's time to replace the spark plug. To check if the spark plug is faulty, use a spark plug tester. A healthy spark plug will produce a strong spark between the tester's terminals during engine cranking. If there's no spark, it means the spark plug is defective and needs replacement.
How to Replace Lawn Mower Spark Plug
- Disconnect the spark plug wire - Locate the spark plug wire, which runs from the spark plug to the magneto or electronic ignition module. Pull the boot off the end of the wire to disconnect it from the spark plug.
- Remove the old spark plug - Using the appropriate size spark plug socket or wrench, loosen the old spark plug by turning it counterclockwise. Once it is loose, unscrew it completely and pull it out of the engine.
- Inspect the old spark plug - Check the condition of the old spark plug. Look for signs of wear like erosion or buildup on the electrodes. This can help diagnose engine issues. Clean any dirt or debris from the spark plug threads.
- Gap the new spark plug - Use a spark plug gap tool to gap the new spark plug to the manufacturer's specified gap, usually between 0.020 and 0.060 inches. Adjust the side electrode to achieve the proper gap.
- Install the new spark plug - Carefully thread the new spark plug into the engine by hand until it is finger tight. Then use the socket or wrench to tighten it another 1/4 to 1/2 turn, being careful not to overtighten.
- Reconnect the spark plug wire - Push the boot back onto the end of the spark plug wire, connecting it securely to the top of the new spark plug.
- Start the engine and test - With the new spark plug installed, try to start the engine. If it starts up smoothly, the spark plug replacement was successful.
2Lawn Mower Primer Bulb
Most Common Solution
Repair Instructions:
As time passes, the primer bulb's rubber can harden and develop cracks. When cracked, air seeps into the fuel system, interfering with the engine's operation. If you notice a cracked primer bulb, it's best to replace it.
How to Replace Lawn Mower Primer Bulb
- Disconnect spark plug wire - Locate the spark plug wire and detach it from the spark plug to prevent accidental starting.
- Drain fuel tank - Use a siphon to empty the gas from the fuel tank into an approved container.
- Detach fuel line(s) - Remove the fuel line(s) from the old primer bulb by squeezing the retainer clips and gently pulling.
- Remove primer bulb - Unscrew or pop out the retaining nut/clip and remove the old primer bulb from the shroud/housing.
- Install new bulb - Position the replacement primer bulb into the housing aligning the fuel line ports.
- Secure primer bulb - Reinstall any retainer clips or screws to mount the new primer bulb into place. Do not overtighten.
- Reconnect fuel lines - Push the fuel line(s) firmly onto the nipples on the new primer bulb. Make sure they click securely into place.
- Refill fuel tank - Pour fresh gas back into the empty fuel tank as needed to resume operation.
- Reconnect spark plug - Reattach the spark plug wire once the new primer bulb is installed.
- Test operation - Press the new primer bulb a few times and check for leaks before starting the mower.
3Lawn Mower Carburetor
Most Common Solution
Repair Instructions:
A clogged carburetor could be the problem. This often happens when fuel sits in the hedge trimmer for too long. As time passes, some fuel components may evaporate, resulting in a dense, sticky residue. This residue can block the carburetor, making the engine difficult to start. If you suspect a clogged carburetor, try cleaning it with a specialized carburetor cleaner. If a simple cleaning doesn't solve the issue, consider rebuilding or replacing the carburetor.
How to Replace Lawn Mower Carburetor
- Disconnect the spark plug wire - Locate the spark plug wire and detach it from the spark plug. This will prevent accidental starting while working.
- Drain the gas tank - Use a siphon or tip the mower to drain all gasoline from the fuel tank into an approved gas container. This minimizes spillage when removing the carburetor.
- Remove air filter - Take out the air filter housing and remove the air filter element. This allows access to the carburetor.
- Detach fuel line - Locate the fuel supply line attached to the carburetor inlet and disconnect it using pliers. Cap the end of the fuel line.
- Remove carburetor retaining nuts - Use a socket or wrench to loosen the carburetor retaining nuts attaching it to the engine intake manifold.
- Detach choke and throttle links - Remove any fasteners or rings connecting the choke and throttle controls from the carburetor levers.
- Lift off the old carburetor - Carefully lift the carburetor off of the intake manifold studs. Take care not to bend or damage linkages.
- Install new carburetor - Place the new carburetor onto the intake manifold studs. Reattach the choke, throttle, fuel line, air filter housing and retaining nuts.
- Reconnect spark plug wire - Attach the spark plug wire to the spark plug once done.
- Test operation - Add fresh gasoline to the fuel tank. Try starting the mower to ensure proper carburetor operation before fully reassembling. Make adjustments as needed.
4Lawn Mower Carburetor Repair Kit
Most Common Solution
Repair Instructions:
The carburetor could be blocked. This usually happens when fuel is left in the hedge trimmer for too long. Over time, some fuel elements can evaporate, creating a thick, sticky material. This gummy substance can obstruct the carburetor, making it difficult to start the engine. If you think the carburetor is blocked, attempt to clean it with a carburetor cleaner. If cleaning doesn't work, you may need to either rebuild or replace the entire carburetor.
How to Replace Lawn Mower Carburetor Repair Kit
- Remove air filter - Detach the air filter housing and remove the air filter element to access the carburetor.
- Drain fuel - Empty the gas from the fuel tank using a siphon or by tipping the mower. This reduces spillage when removing carburetor.
- Detach fuel line - Use pliers to disconnect the fuel supply line from the carburetor inlet. Cap the fuel line.
- Remove carburetor - Take out the retaining nuts and detach any choke/throttle links to fully remove the carburetor.
- Disassemble carburetor - Taking care to organize parts, fully disassemble the carburetor by removing gaskets, jets, float and needle.
- Clean carburetor parts - Use carburetor cleaner spray and small wire brushes to clean all removable parts and passages.
- Install new parts - Replace old gaskets, seals, and worn components with matching parts from the repair kit.
- Reassemble carburetor - Following proper assembly procedures, reinstall float, needle, jets, gaskets and other parts into the cleaned carburetor.
- Install carburetor - Mount the rebuilt carburetor back onto the engine and reconnect fuel line, air filter, choke/throttle links.
- Test operation - Add fresh gas to the fuel tank. Try starting the mower to ensure proper carburetor operation. Make adjustments as needed.
5Lawn Mower Fuel Pump
Common Solution
Repair Instructions:
The fuel pump in a lawnmower has three parts: the gas in port, the gas out port, and the pulse port. The pulse port connects to the engine crankcase via a small rubber tube. As the engine operates, the air in the crankcase fluctuates in pressure, moving a diaphragm in the pump to circulate the gas. If there's too much engine oil, it can seep into the pulse port line and disrupt its function. The fuel pump also has two small valves at the input and output ports to stop fuel from going back into the gas tank - these valves can fail. To see if the fuel pump is faulty, inspect the pulse port line, check valves, and the diaphragm. If the fuel pump isn't working correctly, it can't be repaired – it needs to be replaced.
How to Replace Lawn Mower Fuel Pump
- Disconnect spark plug wire - Locate the spark plug wire and detach it from spark plug to prevent accidental starting.
- Drain fuel tank - Use a siphon to drain gas from the fuel tank into an approved gas container. This minimizes spillage during fuel pump replacement.
- Detach fuel lines - Use pliers to disconnect the fuel lines attached to the inlet and outlet of the old fuel pump.
- Remove pump mounting - Use wrenches to loosen and remove any nuts or brackets securing the fuel pump to the mower frame or engine.
- Install new pump - Attach the new fuel pump to the mower using the same brackets and hardware. Make sure it is oriented correctly.
- Attach fuel lines - Reconnect the fuel supply and return lines to the inlet and outlet fittings on the new fuel pump. Use clamps to secure.
- Check for leaks - Add fresh gas to the fuel tank. Inspect fuel line connections for any leaks with the new pump installed.
- Reconnect spark plug - Once leaks are fixed, reattach the spark plug wire to the spark plug.
- Test operation - Attempt to start the mower's engine to confirm proper fuel flow and pressure from the replaced pump.
- Adjust as needed - Monitor fuel delivery and make any adjustments to pump position or fuel line routing if flow is inadequate before fully reassembling mower.
6Lawn Mower Flywheel Key
Common Solution
Repair Instructions:
If the generator's engine doesn't start, the issue could be a broken flywheel key. This small metal piece connects to the crankshaft and interacts with the flywheel. If the generator engine abruptly stops, the flywheel key can snap. To check if the flywheel key is broken, you'll need to detach the flywheel from the engine and examine the key. If you find that the flywheel key is indeed broken, it should be replaced.
How to Replace Lawn Mower Flywheel Key
- Disconnect spark plug wire - Locate the spark plug wire and detach it from the spark plug to prevent accidental starting.
- Remove debris cover - Take off any plastic belt/debris covers from around the flywheel, under the mower deck. This allows access to the flywheel.
- Mark flywheel position - Before loosening the nut, mark the position of the flywheel in relation to the crankshaft using a marker. This ensures proper reassembly.
- Loosen flywheel nut - Secure the crankshaft and use a socket wrench to loosen the flywheel retaining nut in a counter-clockwise direction.
- Remove flywheel - With the nut removed, carefully slide the flywheel off the crankshaft.
- Take out old key - Locate and remove the damaged square key from the crankshaft keyway. Clean any debris from the keyway.
- Install new key - Seat the new flywheel key into the crankshaft keyway in the proper orientation.
- Reinstall flywheel - Referring to marks made earlier, realign and slide the flywheel onto the crankshaft, seating it properly.
- Tighten flywheel nut - Thread the retaining nut onto the crankshaft and tighten securely with a socket wrench.
- Reconnect spark plug - Once fully reassembled, attach the spark plug wire back to the spark plug. Test start the mower to verify proper flywheel/engine timing with the new key.
7Lawn Mower Ignition Coil
Common Solution
Repair Instructions:
The ignition coil is responsible for supplying voltage to the spark plug when the engine is in operation. If it's faulty, starting the engine might be difficult. Before you replace the ignition coil, make sure the spark plug is functioning correctly. Once you've verified that the spark plug is in good condition, use an ignition coil tester to check the ignition coil. If the test shows that the ignition coil is not working as it should, you'll need to replace it.
How to Replace Lawn Mower Ignition Coil
- Disconnect spark plug wire - Locate the spark plug wire and detach it from the spark plug to prevent accidental starting.
- Remove coil mounting - Use wrenches to loosen and remove any bolts or screws securing the ignition coil to the engine.
- Disconnect wires - Label and detach the primary and secondary coil wires from the ignition system wiring harness.
- Install new coil - Attach the new ignition coil to the engine using the same mounting bolts. Tighten securely.
- Reconnect wires - Referring to labels made earlier, reconnect the primary and secondary coil wires to the proper terminals on the wiring harness.
- Inspect connections - Make sure all wire connections are securely attached and properly routed with no risk of touching hot or moving engine parts.
- Reconnect spark plug - Attach the spark plug wire to the spark plug once the new coil is installed.
- Test operation - Attempt to start the mower to ensure the new coil is firing the spark plug properly before fully reassembling the mower.
- Replace if issues - If the engine fails to start, double check all wiring connections to the new ignition coil. Make sure the air gap is properly set.
8Lawn Mower Fuel Filter
Common Solution
Repair Instructions:
The fuel filter could be blocked, often caused by leaving old fuel in the lawnmower for too long. As time passes, some parts of the fuel can evaporate, creating a dense, adhesive residue. This gummy substance can block the fuel filter, making the engine tough to start. If you left old fuel in the lawnmower, you should drain it from the fuel tank and change the fuel filter.
How to Replace Lawn Mower Fuel Filter
- Disconnect spark plug wire - Locate the spark plug wire and detach it from the spark plug to prevent accidental starting.
- Locate fuel filter - The fuel filter is typically along the fuel supply line somewhere between the gas tank and carburetor.
- Pinch fuel line - Use pliers to clamp off the fuel line on either side of the old filter to minimize gasoline leakage.
- Remove fuel lines - Slide the fuel lines off of the old filter's inlet and outlet nipples. Discard old filter.
- Install new filter - Slide fuel lines onto the corresponding nipples on new filter, following direction of fuel flow.
- Secure fuel lines - Use hose clamps or other fasteners to securely attach fuel lines onto the new filter.
- Check for leaks - Add gas to tank, then inspect fuel line connections at new filter for any leaks. Fix as needed.
- Reconnect spark plug - Once no leaks are found, reattach the spark plug wire to the spark plug.
- Start mower - Attempt to start the mower's engine to verify proper fuel flow through the replaced filter.
- Check filter periodically - Visually inspect new filter occasionally when changing oil for blockage or corrosion.
9Lawn Mower On-Off Switch
Common Solution
Repair Instructions:
The On-Off switch is also known as the ignition switch. It governs the electrical connection from the mower's battery to the ignition system, sparking the fuel in the engine to initiate operation. When the lawn mower is hard to start, a faulty ignition switch could be the cause. A defective switch can disrupt the electricity flow, preventing the spark needed to ignite the fuel, resulting in the engine failing to start or requiring multiple attempts. This can lead to more significant mechanical issues over time. To determine if the On-Off switch is defective, you can use a multimeter to test it for continuity.
How to Replace Lawn Mower On-Off Switch
- Disconnect spark plug wire - Locate the spark plug wire and detach it from the spark plug to prevent accidental starting.
- Remove cover - Take off switch housing cover to access wiring connections.
- Disconnect wires - Label and remove the wire leads from the terminals on the old on/off switch.
- Unmount switch - Remove any mounting screws or nuts to detach the faulty switch from the mower handle.
- Install new switch - Position the replacement on/off switch in the same spot and orient the terminals properly.
- Remount switch - Reinstall any mounting screws or nuts to secure the new switch in place. Do not overtighten.
- Reconnect wires - Attach the wire leads to the correct terminals on the new on/off switch as labeled.
- Replace cover - Reattach switch housing cover once wiring is complete.
- Reconnect spark plug wire - Reattach the spark plug wire to test operation of new switch.
- Verify operation - Turn mower on/off using the replaced switch to ensure proper function.
10Lawn Mower Rewind Spring
Common Solution
Repair Instructions:
The rewind spring is responsible for winding the starter rope back onto a pulley when it's pulled and let go. If this spring is broken, the rope won't wind back onto the pulley, preventing the engine from starting. If the rewind spring is damaged, it needs to be replaced. While many rewind springs can be replaced separately, it might be simpler to replace the entire recoil starter assembly.
How to Replace Lawn Mower Rewind Spring
- Disconnect spark plug wire - Locate the spark plug wire and detach it from the spark plug to prevent accidental starting.
- Remove starter housing - Use screwdrivers to take off the starter rope guide and any covers enclosing the recoil starter assembly.
- Detach rope guide - Unscrew or pop out the guide that the starter rope feeds through on the starter pulley.
- Release spring tension - Gently unwind the existing spring by turning the pulley until slack. Caution - wear eye protection in case it breaks.
- Remove old spring - Detach the old spring from its mounting lugs on the starter housing and pulley. Discard appropriately.
- Install new spring - Hook each end of the new rewind spring into the attachment points. Follow spring wind direction.
- Wind new spring - Carefully wind the pulley clockwise several turns until slight tension is felt when turning it counter-clockwise.
- Reattach rope guide - Screw the rope guide back into the starter pulley , leaving just enough slack for rope to pull freely.
- Replace housing - Reinstall the starter housing covers and starter rope handle.
- Reconnect spark plug wire - Attach the spark plug wire once the new spring is reassembled. Test for smooth pull starting.
11Lawn Mower Rewind Pulley and Spring
Common Solution
Repair Instructions:
The rewind spring plays a crucial role in winding the starter rope back onto a pulley when it's pulled and released. If the rewind spring is broken or the rewind pulley is worn out, the rope will not be able to wind back properly. This issue prevents the engine from starting. While it's possible to replace many rewind springs individually, it might be simpler to replace the entire recoil starter assembly.
How to Replace Lawn Mower Rewind Pulley and Spring
- Disconnect spark plug wire - Locate the spark plug wire and detach it from the spark plug to prevent accidental starting.
- Remove starter housing - Use screwdrivers to take off any covers enclosing the recoil starter assembly to expose the pulley/spring.
- Release spring tension - Carefully unwind the old spring by turning the pulley until loose. Wear eye protection in case it breaks.
- Detach rope handle - Remove screw or clip attaching recoil starter rope handle to old pulley. Slide handle off.
- Remove pulley - Take out screw(s) securing pulley to starter assembly. Detach old pulley and discard appropriately.
- Install new pulley - Secure new starter pulley in place with original mounting screw(s). Make sure it spins freely.
- Attach new spring - Anchor ends of the replacement spring into mounting points following the wind direction.
- Wind new spring - Turn the new pulley clockwise several rotations to tension the spring. Add a little counter-tension.
- Replace rope handle - Slide recoil handle onto new pulley and secure with original clip or screw.
- Reassemble housing - Reinstall starter housing covers. Reconnect spark plug wire once fully reassembled.
12Lawn Mower Recoil Spring
Common Solution
Repair Instructions:
The recoil spring is responsible for rewinding the starter rope onto a pulley when it's pulled and let go. If this spring is broken, the rope can't wind back correctly, preventing the engine from starting. If the recoil spring is damaged, it needs to be replaced. Although many recoil springs can be replaced on their own, it might be simpler to replace the entire recoil starter assembly.
How to Replace Lawn Mower Recoil Spring
- Disconnect spark plug wire - Locate the spark plug wire and detach it from the spark plug to prevent accidental starting.
- Remove starter cover - Use screwdrivers to take off any housing covering the recoil starter assembly to expose spring.
- Release spring tension - Carefully unwind the old recoil spring by turning the pulley until loose. Wear eye protection in case it breaks.
- Detach spring ends - Remove each end of the spring from its mounting point on the starter housing and pulley.
- Install new spring - Hook each end of the replacement recoil spring into the correct attachment points. Follow spring wind direction.
- Wind new spring - Turn the pulley clockwise several rotations to pre-tension the new spring properly. Add a little counter-tension.
- Check pulley/rope - Make sure pulley and starter rope can still retract smoothly without binding once tensioned.
- Replace starter cover - Reinstall any shrouds or housings removed from around recoil starter assembly.
- Reconnect spark plug - Attach the spark plug wire to the spark plug once fully reassembled.
- Test starter - Pull the starter rope to verify smooth retraction with the new spring. Adjust tension as needed.
13Lawn Mower Recoil Starter
Common Solution
Repair Instructions:
The recoil spring helps retract the starter rope onto a pulley when the rope is pulled and then released. If this spring is broken, the rope can't rewind onto the pulley, causing the engine not to start. While it's possible to replace many recoil springs independently, it might be more straightforward to replace the entire recoil starter assembly.
How to Replace Lawn Mower Recoil Starter
- Disconnect spark plug wire - Locate the spark plug wire and detach it from the spark plug to prevent accidental starting.
- Remove starter housing - Use screwdrivers to take off any covers or shrouds enclosing the recoil starter to access assembly.
- Detach pulley and spring - Remove mounting screws to detach the pulley/spring from the starter housing. Retain mounting hardware.
- Disconnect starter - Take out starter mounting bolts and detach recoil assembly from engine block.
- Install new starter - Position the new starter in place against the engine block and secure with original mounting bolts.
- Reattach pulley/spring - Anchor the pulley and recoil spring assembly onto new starter using retained hardware.
- Replace housing - Reinstall any previously removed protective covers or shrouds around starter.
- Reconnect spark plug - Attach the spark plug wire to the spark plug once fully reassembled.
- Test operation - Pull the starter rope to ensure smooth operation of the new recoil starter before fully reassembling mower.
- Adjust as needed - If issues with retracting, adjust pulley and spring so rope recoils correctly.
14Lawn Mower Pre-Cleaner
Rare Solution
Repair Instructions:
If your lawn mower isn't starting easily, it could be due to a blocked air filter pre-cleaner, though this doesn't happen often. To fix this, first, you need to remove the pre-cleaner. Then, make sure you clean it well and thoroughly to ensure proper airflow.
How to Replace Lawn Mower Pre-Cleaner
- Locate pre-cleaner - The pre-cleaner is typically found on top of the air filter housing assembly.
- Remove cover - Take off the air filter cover to access the pre-cleaner.
- Detach pre-cleaner - Remove any retaining clips or screws securing the pre-cleaner. Carefully pull it off.
- Clean housing - Use compressed air to blow out any debris inside the air filter housing.
- Install new pre-cleaner - Place the replacement pre-cleaner into the air filter housing opening.
- Secure pre-cleaner - Reinstall any retaining clips or screws to affix the new pre-cleaner into place.
- Replace cover - Put the air filter cover back on, ensuring it seals properly.
- Check operation - Start the mower engine and let it run for a few minutes, then turn it off and check for dirt bypassing the new pre-cleaner.
- Make adjustments - If needed, open cover and adjust pre-cleaner to sit more flush against housing.
- Change regularly - Check and replace pre-cleaner frequently to maintain engine protection.
15Lawn Mower Recoil Starter Pulley
Repair Instructions:
The recoil starter pulley is responsible for winding the starter rope when it's not being used. If this pulley is damaged or jammed, it won't be able to wind the rope back in. This issue can prevent the engine from starting. If the recoil starter pulley is broken, you'll need to replace it.
How to Replace Lawn Mower Recoil Starter Pulley
- Disconnect spark plug wire - Locate the spark plug wire and detach it from the spark plug to prevent accidental starting.
- Remove starter cover - Use screwdrivers to take off any housing enclosing the recoil starter to access pulley.
- Release spring tension - Carefully unwind the spring by turning the pulley counter-clockwise until loose. Wear eye protection.
- Detach rope handle - Remove screw or clip attaching recoil rope handle to old pulley. Slide handle off.
- Remove pulley - Take out screws/bolts securing pulley to starter. Detach old pulley and discard appropriately.
- Install new pulley - Secure replacement pulley to starter with original hardware. Make sure it spins freely.
- Reattach rope handle - Slide rope handle into new pulley hub and secure with original clip or screw.
- Rewind spring - Wind the pulley clockwise several rotations to re-tension spring. Add a little counter-tension.
- Replace starter cover - Reinstall any previously removed shrouds or housings around the recoil starter.
- Reconnect spark plug - Attach spark plug wire once new pulley is fully installed. Test for smooth retraction.
16Old or Bad Gasoline
Repair Instructions:
The carburetor float bowl could contain old or deteriorated fuel. As time passes, certain fuel components can evaporate, resulting in a dense, adhesive residue. This gummy substance can block the carburetor, making the engine tough to start. If you suspect a clogged carburetor, attempt to clean it using a carburetor cleaner. If cleaning doesn't resolve the issue, it may be necessary to rebuild or replace the entire carburetor.
How to Replace Old or Bad Gasoline
- Disconnect spark plug wire - Locate the spark plug wire and detach it from the spark plug to prevent accidental starting.
- Drain old fuel - Siphon gas from the fuel tank into an approved container. Or tip the lawn mower to pour out old fuel through the fill spout.
- Remove fuel filter - Locate the fuel filter along the supply line and use pliers to detach the fuel lines on both sides. Remove the old filter.
- Replace fuel filter - Attach new fuel filter to supply line with clamps, following direction of fuel flow.
- Flush fuel tank - Mix a fuel tank cleaning solution with some fresh gas in the empty tank. Shake vigorously, drain, and repeat until clean.
- Add new stabilizer - Pour fresh, clean unleaded gas back into the tank. Add fuel stabilizer to prolong shelf life.
- Reconnect spark plug - Reattach the spark plug wire to the spark plug once finished.
- Test mower - Attempt to start the mower to ensure fresh fuel flows through entire system. Check for leaks.
- Consider long-term storage - For mowers that won't be used for extended time, drain gas tank and run engine dry to prevent gumming.