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Lawn Mower is Hard to Start

The lawn mower small 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 18 most common part(s) or condition(s) which contribute to the symptom Lawn mower is hard to start are listed below. Check or test each item and watch any available videos. If you are still unable to solve the problem you may need to do additional research and troubleshooting. Remember, with our 365 Days. Period.® return policy you can return any part for any reason. So, go ahead and buy it to try it. No other parts retailer offers this unconditional return policy.


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For the symptom you selected, these are the most common parts or causes, ordered by the likelihood of fixing the symptom.

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Carburetor

If the lawn mower engine is hard to start it might be getting too much fuel or not enough fuel. In either case, start with the carburetor. If the carburetor is clogged with varnish deposits from old fuel, or if the choke isn't closing properly the engine is hard to start. Try draining all of the old fuel from the carburetor and gas tank. Use fresh fuel with a stabilizer.

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Primer Bulb

If the lawn mower engine is hard to start, check the primer bulb. Over time the rubber of the primer bulb can become brittle and cracked. If the primer bulb lets air into the fuel system the engine will not run properly.

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Carburetor Kit

If the engine is hard to start it might be getting too much fuel or not enough fuel. In either case start with the carburetor. If the carburetor is clogged with varnish deposits from old fuel, or if the choke isn't closing properly the engine is hard to start. Try draining all of the old fuel from the carburetor and gas tank. Use fresh fuel with a stabilizer. If that doesn't do the trick, rebuild the carburetor with this carburetor kit.

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Other Causes and Conditions

Old or Bad Gasoline

If the lawn mower is hard to start, the carburetor might be clogged or have old or bad fuel in the float bowl. If old or bad fuel was left in the lawn mower for a long time some of the volatile ingredients may have evaporated, leaving a thicker, stickier product that is more like varnish or shellac. This sticky fuel can clog up the small jets and ports in the carburetor and it can be difficult to burn making the engine run poorly. The only solution is to drain the old or bad fuel from the float bowl and thoroughly clean the carburetor with carburetor cleaner. If that isn't effective, replace the entire carburetor.

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Spark Plug

If the lawn mower engine is hard to start the spark plug might be defective. All small engines have an ignition coil. The coil is the device that provides spark for the spark plug(s). If the coil is bad power won't get to the spark plug(s). The coil is essentially a small, induction generator. It is mounted next to the flywheel. The flywheel has one or more strong, embedded magnets. As the flywheel spins, the magnet(s) zip past the induction coil, this action of a magnet passing past a coil induces a voltage. Depending on the design of the coil and the strength of the magnets, a stronger or weaker spark can be created and delivered to the spark plug(s). Each time the flywheel spins around a spark is generated. The best way to test a spark plug is to use a spark plug tester. The spark plug should have a strong, visible spark between the electrodes when the engine is cranking. If it doesn't, replace it.

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Fuel Pump Kit

If the lawn mower is hard to start the fuel pump might not be working properly. The fuel pump has three ports, gas in, gas out, 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 which moves a diaphragm inside the pump and pumps the gas. The fuel pump also has two small check valves on the input and output ports to prevent fuel from going back to the gas tank. If the engine oil is overfilled, oil can get into the pulse port line, preventing it from working properly. Also, either of the check valves and the mechanical diaphragm inside the pump can fail. If the pump is not working properly, replace it, it's not possible to repair it. Be certain to replace all parts in this fuel pump kit.

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Fuel Pump

If the lawn mower engine is hard to start the fuel pump might not be working properly. The fuel pump has three ports, gas in, gas out, 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 which moves a diaphragm inside the pump and pumps the gas. The fuel pump also has two small check valves on the input and output ports to prevent fuel from going back to the gas tank. If the engine oil is overfilled, oil can get into the pulse port line, preventing it from working properly. Also, either of the check valves and the mechanical diaphragm inside the pump can fail. If the pump is not working properly it will have to be replaced, it's not possible to repair it.

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Flywheel Key

If the lawn mower is hard to start the flywheel key might have sheared in half. The flywheel key is a small metal shim which fits into a slot in the crankshaft and engages with the flywheel. If the lawn mower blade hits a rock or other solid object the sudden stoppage of the blade can cause the flywheel key to shear. The only way to know for sure if this is the problem is to remove the flywheel and inspect the flywheel key.

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Ignition Coil

If the lawn mower engine is hard to start the ignition coil might be defective. All small engines have an ignition coil. The coil is the device that provides spark for the spark plug(s). If the coil is bad, power won't get to the plug(s). The coil is essentially a small, induction generator. It is mounted next to the flywheel. The flywheel has one or more strong, embedded magnets. As the flywheel spins, the magnet(s) zip past the induction coil, this action of a magnet passing past a coil induces a voltage. Depending on the design of the coil and the strength of the magnets, a stronger or weaker spark can be created and delivered to the spark plug(s). Each time the flywheel spins around a spark is generated. The best way to test the ignition coil is to use a spark plug tester to see if the spark plug is getting a spark. If it is, the ignition coil is working properly.

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Fuel Filter

If the lawn mower is hard to start the fuel filter might be clogged. The fuel filter is usually inline with the fuel line coming from the gas tank. Its purpose is to trap sediment and contaminants from the fuel. Over time it can become clogged and not let enough fuel through. It can't be cleaned but must be replaced if needed.

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On - Off Switch

If the lawn mower engine is hard to start the on/off switch might be turned off or defective. Test the switch with an Ohm meter or continuity checker.

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On-Off Switch

If the lawn mower engine is hard to start the on-off switch might be turned off or defective. Test the switch with an Ohm meter or continuity checker.

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Rewind Spring

When the starter rope is pulled and let go the rewind spring is supposed to recoil the rope onto a pulley. If the rewind spring is broken the rope can't be recoiled onto the pulley which will prevent it from turning over the engine, and then it is hard to start. Many rewind springs can be replaced but it's sometimes easier to replace the whole recoil starter assembly.

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Rewind Pulley and Spring

When the starter rope is pulled and let go the rewind pulley and spring is supposed to recoil the rope onto the pulley. If the recoil spring is broken the rope can't be recoiled onto the pulley which will prevent it from turning over the engine, and then it is hard to start. Many recoil springs can be replaced but it's sometimes easier to replace the whole rewind pulley and spring assembly.

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Recoil Spring

When the starter rope is pulled and let go the recoil spring is supposed to recoil the rope onto a pulley. If the recoil spring is broken the rope can't be recoiled onto the pulley which will prevent it from turning over the engine, and then it is hard to start. Many recoil springs can be replaced but it's sometimes easier to replace the whole recoil starter assembly.

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Recoil Starter

When the starter rope is pulled and let go the recoil starter assembly is supposed to recoil the rope onto a pulley. If the recoil starter assembly is broken the rope can't be recoiled onto the pulley which will prevent it from turning over the engine, and then it is hard to start. Many recoil starter assemblies can be repaired but it's sometimes easier to replace the whole recoil starter assembly.

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Recoil Starter Pulley

When the starter rope is pulled and let go the recoil starter assembly is supposed to recoil the rope onto the recoil starter pulley. If the recoil starter assembly is broken the rope can't be recoiled onto the pulley which will prevent it from turning over the engine, and then it is hard to start. Many recoil starter assemblies can be repaired but it's sometimes easier to replace the whole recoil starter assembly.

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Pre 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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