Honda TRX FOURTRAX FOREMAN RUBICON 2019 Owner's Manual page 170

Spark Plug
8. With the plug washer attached, thread the spark plug in by hand
to prevent cross-threading.
9. Tighten the spark plug:
• If the old plug is good:
1/8 turn after it seats.
• If installing a new plug, tighten it twice to prevent loosening:
a) First, tighten the plug:
NGK:
DENSO: 1/2 turn after it seats.
b) Then loosen the plug.
c) Next, tighten the plug again:
1/8 turn after it seats.
NOTICE
An improperly tightened spark plug can damage the engine. If a
plug is too loose, the piston may be damaged. If a plug is too tight,
the threads may be damaged.
10. Connect the spark plug cap. Take care to avoid pinching any
cables or wires.
11. Install the remaining parts in the reverse order of removal.
160 Servicing Your Honda
3/4 turn after it seats.