MODEL-AWARE TROUBLESHOOTING
John Deere S100 cranks but won’t start
A cranking engine has passed part of the starting circuit, so test fuel, spark, and airflow without guessing at parts. This guide is mapped to mower model S100 / BG21416 and its 31R977 (M31) engine configuration.
Make the machine safe firstWork outdoors. Park on level ground, disengage the blades, set the brake, remove the key before touching components, and let hot parts cool. Follow the manufacturer manual. Do not bypass safety switches.
First checks that preserve the evidence
- Confirm the tank has fresh gasoline and the fuel shutoff, if fitted, is open.
- Inspect the air-filter area for blockage or liquid fuel before attempting any spark test.
- Use the guided diagnosis to choose one safe test at a time and record what changes.
Continue with a guided diagnosis
Detayl uses your observations to select the next useful check. Its scoring and test-selection logic remain on the server; this page does not publish the diagnostic graph.
Diagnose this mower