1981-1984 Official Honda ATC250R Shop Manual, Page 137Get this manual
r::iJ HONDA ATC 250R
BRAKE MECHANISM (FRONT DISC BRAKE)
Operate the brake lever to force the piston out from the cylinderNOTE Place an oil pan under the caliper to receive drained brake flu idAvoid spilling brake fluid on painted surfaces, plastic lenses or rubber parts
CALIPER PISTON AIR NOZZLE Disconnect the brake hose from the caliperIf the piston is stuck in the caliper, do the following stepsPlace shop towel or rag over the piston to prevent the piston and brake fluid from coming out, and apply small amount of air pressure to the fluid inlet