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HomeRepair HelpMower RepairLawn mower runs rough Repair
Lawn mower runs rough
If your lawn mower runs rough, sputters, or surges after starting, the problem is usually in the fuel system, with a clogged carburetor at the top of the list. Old fuel can leave behind a sticky residue that blocks passages in the carburetor and makes the engine run unevenly. Start by cleaning the carburetor with carburetor cleaner. If that does not fix the issue, rebuild it with a carburetor repair kit or replace the carburetor altogether. Next, check the spark plug. A worn plug, cracked insulator, damaged electrode, or heavy carbon buildup can all make a lawn mower run rough, and a spark plug tester can help confirm whether the plug is producing a strong spark. After that, inspect the fuel filter, since stale fuel can clog the filter and restrict fuel flow enough to cause rough running. Whether you have a Honda, Toro, Craftsman, Husqvarna, MTD, Troy-Bilt, Cub Cadet, or another mower brand, enter your model number on RepairClinic.com to find the exact replacement carburetor, carburetor repair kit, spark plug, or fuel filter for your machine.
01 - Lawn Mower 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.
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02 - Lawn Mower 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 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.
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03 - Lawn Mower 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.
Highly Likely
04 - Lawn Mower Fuel 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 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.
Less Common
Frequently Asked Questions
Why does my lawn mower run rough after it starts?
Can old gas make a mower engine surge or sputter?
How do I know if the spark plug is causing my lawn mower to run rough?
Should I clean, rebuild, or replace the carburetor if my mower runs rough?
How do I find the right carburetor, carburetor repair kit, spark plug, or fuel filter for my mower?