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My lawn mower won't start

You've got a yard full of grass that that should have been cut last week only to find that your lawn mower won't start. Instead of giving up and letting the grass take over, allow Repair Clinic to help you get your yard back on track. There are many reasons that can stop your lawn mower from starting. You may need new spark plugs or a new carburetor. Or, the fuel in the mower may be old. Regardless of why your lawn mower isn't starting, Repair Clinic is here to help troubleshoot and diagnose the issue. We also have repair videos that give you step-by-step directions and the necessary replacement parts. Your DIY fix will not only save you money but return your lawn to the neat green oasis you're used to.
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Common solutions for: Lawn mower won't start
Solution 1:
Spark Plug
Inspect the spark plug for signs of wear or damage. If the porcelain insulator is cracked, an electrode is burned away or damaged, or there is heavy carbon buildup at the electrode, replace the spark ...plug. To determine if the spark plug is defective, use a spark plug tester. You should see a strong spark between the tester’s terminals when the engine is cranking. If there is no spark, this indicates that the spark plug is defective and should be replaced.
Required Part
Lawn Mower Spark Plug
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Solution 2:
Carburetor
The carburetor might be clogged. A clogged carburetor is most commonly caused by leaving fuel in the lawn mower for a long period of time. Over time, some of the ingredients in the fuel may evaporate,... leaving behind a thicker, stickier substance. This sticky fuel can clog up the carburetor and prevent the engine from starting. If the carburetor is clogged, try cleaning it with carburetor cleaner. If cleaning the carburetor isn’t effective, rebuild or replace the entire carburetor.
Required Part
Lawn Mower Carburetor
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Solution 3:
Carburetor Repair Kit
The carburetor might be clogged. A clogged carburetor is most commonly caused by leaving fuel in the lawn mower for a long period of time. Over time, some of the ingredients in the fuel may evaporate,... leaving behind a thicker, stickier substance. This sticky fuel can clog up the carburetor and prevent the engine from starting. If the carburetor is clogged, try cleaning it with carburetor cleaner. If cleaning the carburetor isn’t effective, rebuild or replace the entire carburetor.
Required Part
Lawn Mower Carburetor Repair Kit
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Solution 4:
Old or Bad Gasoline
There may be old or bad fuel in the carburetor float bowl. Over time, some of the ingredients in the fuel may evaporate, leaving behind a thicker, stickier substance. This sticky fuel can clog up the carburetor and prevent the engine from starting. If the carburetor is clogged, try cleaning it with carburetor cleaner. If cleaning the carburetor isn’t effective, rebuild or replace the entire carburetor.
Solution 5:
Fuel Pump
The fuel pump has three ports: the gas in port, the gas out port, and the pulse port. The pulse port is connected to the engine crankcase by a small rubber tube. As the engine runs, air inside the cra...nkcase alternately pressurizes and depressurizes the air in the tube. This pressurized air moves a diaphragm inside the pump and pumps the gas. If the engine oil is overfilled, oil can enter the pulse port line, preventing it from working properly. The fuel pump also has two small check valves on the input and output ports. The check valves prevent fuel from reentering the gas tank. These check valves can fail. To determine if the fuel pump is defective, check the pulse port line, check valves, and the diaphragm inside the pump. The fuel pump is not repairable—if the fuel pump is not working properly, you must replace it.
Required Part
Lawn Mower Fuel Pump
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Solution 6:
Start Switch
To determine if the start switch is defective, use a multimeter to test it for continuity....
Required Part
Lawn Mower Start Switch
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Solution 7:
Flywheel Key
the flywheel key might have sheared in half. The flywheel key is a small metal piece which fits into the crankshaft and engages with the flywheel. If the lawn mower engine stops suddenly due to hittin...g a hard object, the flywheel key breaks in half to prevent damage to the engine. If the flywheel key is broken, the lawn mower won't start. To determine if the flywheel key is broken, remove the flywheel from the engine and inspect the flywheel key. If the flywheel key is broken, replace it.
Required Part
Lawn Mower Flywheel Key
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Solution 8:
Ignition Coil
The ignition coil sends voltage to the spark plug while the engine is running. If the ignition coil is defective, the engine may not start. Before replacing the ignition coil, ensure that the spark pl...ug is working properly. If you have confirmed that the spark plug is working properly, test the ignition coil with an ignition coil tester. If the ignition coil is defective, replace it.
Required Part
Lawn Mower Ignition Coil
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Solution 9:
Fuel Filter
The fuel filter might be clogged. A clogged fuel filter is most commonly caused by leaving old fuel in the lawn mower. Over time, some of the ingredients in the fuel may evaporate, leaving behind a th...icker, stickier substance. This sticky fuel can clog up the fuel filter and prevent the engine from starting. If old fuel was left in the lawn mower, drain the old fuel from the fuel tank and replace the fuel filter.
Required Part
Lawn Mower Fuel Filter
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Solution 10:
Safety Switch
To determine if the safety switch is defective, use a multimeter to test it for continuity....
Required Part
Lawn Mower Safety Switch
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Solution 11:
Recoil Spring
When the starter rope is pulled and let go the recoil spring is supposed to recoil the rope onto a pulley. If the recoil spring is broken the rope can't be recoiled onto the pulley which will prevent ...it from turning over the engine, and then it does not start. Many recoil springs can be replaced but it's sometimes easier to replace the whole recoil starter assembly.
Required Part
Lawn Mower Recoil Spring
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Solution 12:
Recoil Starter
The recoil starter assembly engages the crankshaft to turn over the engine. If the recoil starter assembly is defective, the engine won't start. Remove the starter assembly and inspect it to determine... if it is working properly. When you pull the starter rope, tabs extending from the pulley and cam should grab the hub on the engine, causing the engine to turn. When you release the rope, the tabs should retract and the rope should rewind back on the pulley. If the recoil starter assembly is not working properly, replace it.
Required Part
Lawn Mower Recoil Starter
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Solution 13:
Recoil Starter Pulley
The recoil starter pulley winds up the starter rope when the rope is not in use. If the recoil pulley is broken or stuck, it won't be able to rewind the starter rope. As a result, the engine won't sta...rt. If the recoil starter pulley is broken, replace it.
Required Part
Lawn Mower Recoil Starter Pulley
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Solution 14:
Rewind Pulley and Spring
The rewind spring might be broken. When the starter rope is pulled and released, the rewind spring recoils the starter rope onto a pulley. If the rewind spring is broken, or if the rewind pulley is wo...rn out, the rope won’t be able to recoil onto the pulley. As a result, the engine won’t start. If the rewind spring is broken, replace it. Many rewind springs can be replaced individually, but it may be easier to replace the entire pulley and spring assembly.
Required Part
Lawn Mower Rewind Pulley and Spring
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Solution 15:
Rewind Spring
The rewind spring might be broken. When the starter rope is pulled and released, the rewind spring recoils the starter rope onto a pulley. If the rewind spring is broken, the rope won’t be able to rec...oil onto the pulley. As a result, the engine won’t start. If the rewind spring is broken, replace it. Many rewind springs can be replaced individually, but it may be easier to replace the entire recoil starter assembly.
Required Part
Lawn Mower Rewind Spring
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