The part(s) or condition(s) listed below for the symptom Lawn mower runs rough 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.
Lawn Mower Leaking Gas? Lawn Mower Troubleshooting
Lawn Mower Not Self-Propelling? Lawn Mower Troubleshooting
Lawn Mower Runs Rough? Lawn Mower Troubleshooting
Lawn Mower Starts Then Stalls? Lawn Mower Troubleshooting
Lawn Mower Won't Start? Lawn Mower Troubleshooting
Riding Mower Blades Won't Engage? Riding Mower Troubleshooting
Lawn Mower Smoking? Lawn Mower Troubleshooting
Lawn Mower Battery Keeps Dying? Lawn Mower TroubleshootingThe 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 cause the engine to run roughly. If the carburetor is clogged, try cleaning it with carburetor cleaner. If cleaning the carburetor isn’t effective, rebuild or replace the entire 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 cause the engine to run roughly. If the carburetor is clogged, try cleaning it with carburetor cleaner. If cleaning the carburetor isn’t effective, rebuild or replace the entire carburetor.
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.
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 cause the engine to run roughly. If old fuel was left in the lawn mower, drain the old fuel from the fuel tank and replace the fuel filter.
