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Lawn Boy Lawn Mower Won't Start

The lawn mowersmall engine often has a separate model number. Use the small engine model number for a complete list of symptoms and parts. Watch our model # lookup video for help finding the model number.

10685/SERIAL: 280000001-280999999

The part(s) or condition(s) listed below for the symptom Lawn mower won't start are ordered from most likely to least likely to occur. Check or test each item, starting with the items at the top of the page.

Most Frequent Causes for Lawn mower won't start

Cause 1Spark 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.

Parts
Spark Plug for your Lawn BoyLawn Mower
Spark Plug - Part # 1863243 Mfg Part # 868

Small engine Champion spark plug (RJ19LM). If the engine does not start, the spark plug may be defective. The spark plug should be replaced periodically during regular maintenance.

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Cause 2Carburetor

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.

Parts
Carburetor for your Lawn BoyLawn Mower
Carburetor - Part # 1727820 Mfg Part # 640350

Tecumseh carburetor kit. If the carburetor is clogged, the engine won't get enough fuel. As a result, the engine may not start or may run rough.

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Cause 3Carburetor 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.

Parts
Carburetor Repair Kit for your Lawn BoyLawn Mower
Carburetor Repair Kit - Part # 1606506 Mfg Part # 631021B

Tecumseh carburetor repair kit. If the carburetor is clogged, the engine won't get enough fuel. As a result, the engine may not start or may run poorly.

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Cause 4Carburetor 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.

Parts
Carburetor Repair Kit for your Lawn BoyLawn Mower
Carburetor Repair Kit - Part # 1659224 Mfg Part # 632760B

Tecumseh carburetor repair kit. If the carburetor is clogged, the engine won't get enough fuel. As a result, the engine may not start or may run rough.

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Cause 5Old 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.

Cause 6Flywheel 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 hitting 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.

Parts
Flywheel Key for your Lawn BoyLawn Mower
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Cause 7Ignition 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 plug 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.

Parts
Ignition Coil for your Lawn BoyLawn Mower
Ignition Coil - Part # 1719806 Mfg Part # 34443D

Tecumseh ignition coil (also called a lamination). 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.

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Cause 8Recoil Starter

When the starter rope is pulled and released, the recoil spring recoils the starter rope onto a pulley. If the recoil spring is broken, the rope won’t be able to recoil onto the pulley. As a result, the engine won’t start. Many recoil springs can be replaced individually, but it may be easier to replace the whole recoil starter assembly.

Parts
Recoil Starter for your Lawn BoyLawn Mower
Recoil Starter - Part # 1659157 Mfg Part # 590739

Small engine recoil starter kit. The starter rope is pulled it causes the starter cogs to engage the drive cup on the flywheel and start the engine.

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Cause 9Recoil Starter

When the starter rope is pulled and released, the recoil spring recoils the starter rope onto a pulley. If the recoil spring is broken, the rope won’t be able to recoil onto the pulley. As a result, the engine won’t start. Many recoil springs can be replaced individually, but it may be easier to replace the whole recoil starter assembly.

Parts
Recoil Starter for your Lawn BoyLawn Mower
Recoil Starter - Part # 1659161 Mfg Part # 590772
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Cause 10Recoil 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 start. If the recoil starter pulley is broken, replace it.

Parts
Recoil Starter Pulley for your Lawn BoyLawn Mower