Replace the gasket if it is damaged.
If they are clogged, remove the tank and drain it, and then blow the breather free with compressed air.

NOTICE
Do not apply compressed air to the air vent holes [D] in the tank cap. This could cause damage and clogging of the labyrinth in the cap.
Fuel Tank Installation
Fuel Tank CleaningCaliper Installation
Install the caliper and brake hose lower end.
For the front caliper, be sure to install the collars [A].
Replace the washers on each side of hose fitting with new
ones.
Touch the brake hoses [A] to the stopper [B] of the caliper.
Front Calipers [C]
Rear Caliper [D]
Tighten:
To ...
Coolant Level Inspection
Situate the motorcycle so that it is
perpendicular to the ground.
Check the coolant level through the
coolant level gauge on the reserve
tank located to the left of the engine.
The coolant level should be between
the “F” (Full) and “L” (Low) level lines.
A. Reserve Ta ...
Air Suction Valve Inspection
Remove the air suction valve (see Air Suction Valve Removal).
Visually inspect the reeds [A] for cracks, folds, warps,
heat damage or other damage.
If there is any doubt as to the condition of the reeds, replace
the air suction valve as an assembly.
Check the reed contact areas [B] of ...