2008 Yamaha Raptor 250SE / 250SE2 Factory Service Manual, Page 93Get this manual
BLEEDING THE HYDRAULIC BRAKE SYSTEM
NOTE: Be careful not to spill any brake fluid or allow the brake master cylinder reservoir or brake fluid reservoir to overflow When bleeding the hydraulic brake system, make sure there is always enough brake fluid before applying the brakeIgnoring this precaution could allow air to enter the hydraulic brake system, considerably lengthening the bleeding procedure If bleeding is difficult, it may be necessary to let the brake fluid settle for few hoursRepeat the bleeding procedure when the tiny bubbles in the hose have disappeared