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HomeRepair HelpRepairLawn mower is hard to start Repair
Lawn mower is hard to start
If your lawn mower is hard to start, the problem is usually in the fuel system first, not the engine itself. The most common cause is a clogged carburetor from stale gas that has turned sticky and restricted fuel flow, which is why a lawn mower difficult to start or a small engine hard to start often improves after cleaning the carburetor with carburetor cleaner. If cleaning does not help, you may need a carburetor repair kit or a complete carburetor replacement. Next, check the primer bulb, since a brittle or cracked bulb can let air into the system and make a lawn mower take many pulls to start. Old or bad gasoline in the carburetor float bowl can cause the same hard-starting symptoms. After that, inspect the spark plug for wear, carbon buildup, or a weak spark, and test it with a spark plug tester if needed. On models equipped with one, a failing fuel pump can also make a mower hard starting by starving the carburetor of fuel. Enter your model number on RepairClinic.com to find the exact carburetor, primer bulb, spark plug, fuel pump, or other lawn mower parts that fit your machine.
01 - Carburetor
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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02 - Primer 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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03 - Carburetor 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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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 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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05 - 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
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
07 - Flywheel 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.
Common
Frequently Asked Questions
Why is my lawn mower hard to start after it has been sitting?
My push mower takes many pulls to start. Should I check the primer bulb first?
My lawn mower has spark but is still hard to start. What else should I check?
How do I know if the fuel pump is causing my lawn mower not to start easily?
How do I find the right carburetor, primer bulb, fuel pump, or spark plug for my mower?