Suzuki GN125F Service Manual page 24

AIR BLEEDING THE BRAKE FLUID CIRCUIT
Air trapped in the fluid circuit acts like a cushion to absorb a
large proportion of the pressure developed by the master
cylinder and thus interferes with the full braking performance
of the caliper brake. The presence of air is indicated by
"sponginess" of the brake lever and also by lack of braking
force. Considering the danger to which such trapped air
exposes the machine and rider, it is essential that, after
remounting the brake and restoring the brake system to the
normal condition, the brake fluid circuit be purged of air in the
following manner:
Fill up the master cylinder reservoir to the upper line.
Replace the reservoir cap to prevent entry of dirt.
Attach a pipe to the caliper bleeder valve, and insert the free
end of the pipe into a receptacle.
Squeeze and release the brake lever several times in rapid
succession, and squeeze the lever fully without releasing it.
Loosen the bleeder valve by turning it a quarter of a turn so
that the brake fluid runs into the receptacle; this will remove
the tension of the brake lever causing it to touch the
handlebar grip. Then close the valve, pump and squeeze the
lever, and open the valve.
Repeat this process until the fluid flowing into the receptacle
no longer contains air bubbles.
CAUTION
Replenish the brake fluid reservoir as necessary while
bleeding the brake system. Make sure that there is
always some fluid visible in the reservoir.
Close the bleeder valve, and disconnect the pipe. Fill the
reservoir to the "upper" level line.
CAUTION
Handle the brake fluid with care: the fluid reacts
chemically with paint, plastics, rubber materials, etc.
FRONT BRAKE LIGHT SWITCH
Squeeze the front brake lever to inspect the brake light switch.
If the brake light switch works inflexible, inspect, adjust or
replace.
PERIODIC MAINTENANCE
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