Fuel Tank Cap With Check Valve - Yamaha XT550J Service Manual

G.
Fuel Tank Cap with Check Valve
The fuel cap has a free steel ball inside it to prevent
fuel from spilling out through the cap breather
should the machine turnover.
This steel ball normally settles at the bottom, but
when the machine is inclined to less than 30° from
the ground as in a turnover, the ball is made to roll
accordingly while at the same time pushing up on
the valve seat (see drawing).
When the machine is laid flat on the ground, the
O-ring on the valve contacts the tapered wall of
the cap, thereby closing the breather passage
completely.
1-8