Yamaha Big Bear Professional YFM400FW Manual Del Propietário página 292

NOTE:
If a torque wrench is not available when you
are installing a spark plug, a good estimate of
the correct torque is 1/4 to 1/2 turn past finger
tight. Have the spark plug tightened to the
specified torque as soon as possible.
4. Install the spark plug cap.
8-41