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Lawn Mower is Hard to 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.

The part(s) or condition(s) listed below for the symptom Lawn mower is hard to 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 is hard to start

For the most accurate results, enter your model number.


Cause 1Carburetor

The carburetor might be clogged. A clogged carburetor is most commonly caused by leaving fuel in the hedge trimmer 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 make the engine hard to start. If the carburetor is clogged, try cleaning it with carburetor cleaner. If cleaning the carburetor isn’t effective, rebuild or replace the entire carburetor.

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Cause 2Primer Bulb

Over time, the rubber of the primer bulb can become brittle and cracked. If the primer bulb is cracked, air will get into the fuel system and cause the engine not to run properly. If the primer bulb is cracked, replace it.

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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 hedge trimmer 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 make the engine hard to start. If the carburetor is clogged, try cleaning it with carburetor cleaner. If cleaning the carburetor isn’t effective, rebuild or replace the entire carburetor.

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Cause 4Old 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 make the engine hard to start. 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 5Spark 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.

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Cause 6Fuel 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 crankcase 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.

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Cause 7Flywheel Key

If the generator engine won’t start, 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 generator engine stops suddenly, the flywheel key may break in half. 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.

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Cause 8Ignition Coil

The ignition coil sends voltage to the spark plug while the engine is running. If the ignition coil is defective, the engine may be hard to 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.

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Cause 9Fuel 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 make the engine hard to start. If old fuel was left in the lawn mower, drain the old fuel from the fuel tank and replace the fuel filter.

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Cause 10On - Off Switch

To determine if the on-off switch is defective, use a multimeter to test it for continuity.

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Cause 11Rewind Spring

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 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 whole recoil starter assembly.

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Cause 12Rewind Pulley and Spring

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 worn out, the rope won’t be able to recoil onto the chainsaw pulley. As a result, the engine won’t start. Many rewind springs can be replaced individually, but it may be easier to replace the whole recoil starter assembly.

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Cause 13Recoil Spring

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. If the recoil spring is broken, replace it. Many recoil springs can be replaced individually, but it may be easier to replace the whole recoil starter assembly.

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Cause 14Recoil 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.

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Cause 15Recoil 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.

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Cause 16Pre-Cleaner

If the lawn mower engine is hard to start the air filter pre cleaner might be clogged. This is rare. Remove the pre cleaner and clean it thoroughly.

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