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John Deere Replacement Part 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.

LA105/42in Deck/Engine: 31P677-0239-B1

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.

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 John Deere Replacement PartLawn Mower
Spark Plug - Part # 1605018 Mfg Part # 71G

Champion Spark Plug (RC12YC). The spark plug ignites the fuel and air mixture in the engine's cylinder to power the engine. If the spark plug is has fouled (if the tip of the spark plug is burnt or damaged), the engine may not start or may run rough.

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Cause 2Old 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 3Ignition 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 John Deere Replacement PartLawn Mower
Ignition Coil - Part # 2120381 Mfg Part # 799650

The ignition coil (armature) supplies voltage to the spark plug as the flywheel rotates. If the engine won’t start, the ignition coil could be defective.

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Cause 4Fuel 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 thicker, 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.

Parts
Fuel Filter for your John Deere Replacement PartLawn Mower
Fuel Filter - Part # 1567882 Mfg Part # 4129

5 pack of Fuel Filter 691035

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Cause 5Fuel 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 thicker, 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.

Parts
Fuel Filter for your John Deere Replacement PartLawn Mower
Fuel Filter - Part # 1567939 Mfg Part # 691035

Briggs and Startton in-line fuel filter with 40 micron rating and 1/4" inlet & outlet. If the engine does not start then the fuel filter may be clogged and not allowing enough fuel to enter the carburetor.

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Cause 6Fuel 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 thicker, 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.

Parts
Fuel Filter for your John Deere Replacement PartLawn Mower