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HomeRepair HelpRepairLawn mower won't start Repair
My lawn mower won't start
If your lawn mower won't start, start with the basics that fail most often. A worn or fouled spark plug is the top suspect, so check for a cracked insulator, damaged electrode, or heavy carbon buildup, and confirm spark with a spark plug tester while the engine is cranking. If the plug checks out, the next most likely problem is a clogged carburetor caused by stale fuel. Old gas can leave sticky deposits in the carburetor and carburetor float bowl, which can keep the engine from firing at all. In many cases, cleaning the carburetor with carburetor cleaner helps, but you may need a carburetor repair kit or a full replacement carburetor. After that, check for old or bad gasoline, then test the start switch for continuity with a multimeter. On models equipped with one, a bad fuel pump can also keep a push mower or riding mower from starting by blocking fuel flow through the pulse line or failed check valves. Whether your lawn mower not starting is a Honda, Toro, Craftsman, Husqvarna, MTD, Cub Cadet, or Troy-Bilt, enter your model number on RepairClinic.com to find the exact replacement part that fits your mower.
01 - 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.
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02 - 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.
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03 - 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.
Top Solution
04 - 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.
Top Solution
05 - Start Switch
To determine if the start switch is defective, use a multimeter to test it for continuity.
Highly Likely
06 - 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 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...
Highly Likely
Frequently Asked Questions
Why won't my lawn mower start even though it has fuel?
How do I tell if the spark plug is the reason my push mower won't start?
Can old gas make a lawn mower not starting problem worse?
How do I check a lawn mower start switch or fuel pump if the engine will not start?
How do I find the right spark plug, carburetor, or fuel pump for my mower on RepairClinic.com?
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