Yamaha BIG BEAR PROFESSIONAL 400 YFM400FPT Owner's Manual page 296

a. Spark plug gap
a. Écartement des électrodes
a. Huelgo de la bujía
Before installing the spark plug, measure the elec-
trode gap with a wire thickness gauge and adjust it
to specification.
Spark plug gap:
0.6–0.7 mm
When installing the spark plug, always clean the
gasket surface and its mating surface. Wipe off
any grime from the threads and tighten it to the
specified torque.
Tightening torque:
Spark plug:
17.5 Nm (1.75 m·kgf)
8-45