Why Does My Lawn Mower Start Then Die?

It’s a beautiful clear afternoon with low humidity; the perfect day to mow your lawn. You find you’re able to start your walk-behind mower or riding mower, but as soon as you begin cutting the grass, the engine suddenly dies. As disappointing as this scenario is, it’s a common one and there are three likely causes for why it happens.

A restricted carburetor can stall an engine

The lawn mower engine carburetor ensures that the proper mixture of fuel and air will enter the engine cylinder to allow for combustion. Old or bad fuel can leave a gummy residue inside the carburetor which can restrict it, preventing the proper ratio of fuel and air from entering the cylinder and stalling the engine. Here are some tips you can follow to fix or prevent this problem:

  • Use WD-40, or a dedicated carburetor cleaner, to clean out the ports on the carburetor.
  • Purchase a carburetor repair kit to replace the float needle, spring, gaskets, and O-rings.
  • If cleaning or replacing certain components is ineffective, you should replace the old carburetor with a new one.
  • Use only fresh fuel when filling the lawn mower fuel tank and add a fuel stabilizer to help maintain the quality of that fuel.

The fuel tank cap can get clogged as well

As fuel is consumed by the lawn mower engine, the level of fuel in the tank lowers and the empty portion of the tank is filled with air. There are small vent holes in the fuel tank cap to allow air to enter the tank for this purpose. However, if these holes become blocked by debris, a vacuum will be created that can cause the engine to stall. While you can attempt to clear out the vent holes, it’s probably easier to simply replace the old fuel cap with a new one.

A worn out spark plug could be the culprit

Due to carbon build-up and a weakened electrode, the engine’s spark plug will wear out over time. If the spark plug is unable to continue sparking to ignite the fuel and air being drawn into the engine cylinder, the engine will suddenly die.

It is recommended that the spark plug be replaced once a year as part of your annual lawn mower engine tune-up. While you should first visually inspect the plug for damage or wear, you can also use an ignition tester to determine if the component is faulty:

  • Remove the ignition coil wire and boot from the spark plug.
  • Attach the ignition tester clip to the spark plug and insert the opposite end of the tester into the boot.
  • Attempt to start the engine but stand clear of the tester or any other electrical component to avoid a shock.
  • If a spark jumps across the terminals in the tester window (or the engine starts), the spark plug and engine ignition coil are working properly.
  • If you do not see a spark, unclip the tester from the spark plug and attach it to a good grounding location like a bolt on the engine valve cover.
  • Attempt to start the engine again.
  • If there is now a spark visible in the tester window, the spark plug is likely defective and will need to be replaced.
  • If there is still no spark in the tester window, the ignition coil may have failed or there may be another problem with the equipment’s electrical system.

Find the right lawn mower parts with Repair Clinic

Repair Clinic stocks all the replacement parts that fit your lawn mower, including carburetors from Briggs and Stratton, Walbro, and Zama. You can also find the exact fuel cap and spark plug that match the mower’s fuel tank and engine, respectively. To find the right part, enter the full model number of your lawn mower, or the mower’s engine, in the Repair Clinic website search bar. While Repair Clinic carries lawn mower parts for all the top brands including Craftsman, Honda, Husqvarna, and Toro, you’ll want to make sure you’re selecting a part that is directly associated with your equipment.

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