How to troubleshoot my lawn mower's ignition

Written by billy ray
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How to troubleshoot my lawn mower's ignition
A faulty ignition on a riding mower is more difficult to troubleshoot than on push mowers. (lawnmower man image by feisty from

When it is time to mow your lawn, it's frustrating that a mower won't start. Troubleshooting a faulty ignition system on a riding lawnmower is more complicated than on push models because they have more components that can go wrong. In addition to needing fuel and a spark, these mowers have kill circuits installed for safety reasons that can also be the culprit. Check all the components yourself and isolate the problem.

Skill level:

Things you need

  • Spark plug wrench
  • Clean cloths
  • Wire brush
  • Spark plug tester tool
  • Filters

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  1. 1

    Inspect the lawnmower and verify that the cut-off switch is on the "On" or "Run" position, there is fresh fuel in the fuel tank and the engine is turning over when the key is turned.

  2. 2

    Check the spark plug for carbon build-up by unscrewing it with the spark plug socket and removing it. Clean the spark plug well with a clean cloth and a wire brush. Use the spark plug checker according to the manufacturer's directions. Look for a strong blue spark on the tester when the engine is being cranked. No spark or a weak yellow spark means the ignition system is not providing enough power for the spark plug to fire properly, usually due to a weak battery or faulty wiring. Replace the spark plug with an appropriate substitute if the plug is getting sufficient spark and still will not start.

  3. 3

    Inspect the battery and wiring if the machine will not turn over. If the engine won't start, it could mean a dead battery, corroded battery posts and connections or faulty wiring. Replace or recharge the battery if the starter won't turn over or struggles to turn over. Clean the posts and cables and verify all the wiring connections are in good condition.

  4. 4

    Check the flywheel key and make sure it is not broken. The flywheel key makes sure the flywheel keyway and the crankshaft keyway are "timed" properly. A broken flywheel key means the motor is not timed properly and this can prevent the mower from starting. Replace this part with an appropriate replacement part if needed.

  5. 5

    Look at your owner's manual and find the location of all the kill circuits on your mower. The wiring may have kill switches under the seat, at the throttle control plate and other spots on your mower that will need to be checked. Verify these circuits are intact and properly functioning. Faulty circuits will make the kill switch engage, which prevents the motor from starting.

  6. 6

    Check the fuel system's lines and filters for blockage, holes or grime. Clean or replace the lines and filters with appropriate parts made to fit your mower. Check the air filter and clean or replace it if necessary. Dirty filters and clogged or leaking fuel lines can prevent the proper fuel and air mixture to be provided for the mower to start.

Tips and warnings

  • The spark plug testing tool can be used to test the kill switch circuits.
  • Do not bypass the kill switches, as this will allow the mower to continue running when it is not designed to do so.

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