Yamaha YFM90RY Owner's Manual page 79

TIP
The air filter needs more frequent service if you are riding in unusually wet or dusty areas.
Hydraulic brake service
Regularly check and, if necessary, correct the brake fluid level.
Every two years replace the internal components of the brake master cylinder and caliper, and
change the brake fluid.
Replace the brake hoses every four years and if cracked or damaged.
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