Suzuki DF25/DF30 Four Stroke Service Manual, Page 35Get this manual
2-8 PERIODIC MAINTENANCE
SPARK PLUG
Inspect every 100 hours (6 months) Replace every 200 hours (12 months)Standard spark plugNGK DCPR6E
Only resistor (R) type spark plugs must be used with this engineUsing non-resistor spark plug will cause ignition system malfunctionsCARBON DEPOSIT Check for carbon deposit on the spark plug basesIf carbon is present, remove it with spark plug cleaning machine or by carefully using pointed tool