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 CleaningExploded View
13. Front Wheel Rotation Sensor
B: Apply brake fluid.
L: Apply a non-permanent locking agent.
R: Replacement Parts
S: Follow the specified tightening sequence.
Si: Apply silicone grease (ex. PBC grease).
10. Rear Wheel Rotation Sensor
B: Apply brake fluid.
G: Apply gr ...
Water Temperature Sensor Removal/Installation
NOTICE
Never drop the water temperature sensor especially
on a hard surface. Such a shock to the sensor can
damage it.
Remove the throttle body assy (see Throttle Body Assy
Removal in the Fuel System (DFI) chapter).
Drain the coolant (see Coolant Change in the Periodic
Maintenance c ...
Throttle Grip and Cables
Free Play Inspection
Refer to the Throttle Control System Inspection in the Periodic
Maintenance chapter.
Free Play Adjustment
Refer to the Throttle Control System Inspection in the Periodic
Maintenance chapter.
Cable Installation
Install the throttle cables in accordance with the Cable,
...