xj650 master cylinder questions

The m/c and caliper may not be the problem. The brake lines and banjo bolts (the fluid travels through them) have to be clean and in good condition. When everything is in order you should be able to set the adjuster nut/bolt for proper play at the perch. The stock m/c has two holes that have to be cleared (use a stripped bread wrapper or trash bag tie to clear the tiny hole) before fluid will shoot back into the m/c. Remember...most of braking is done at the front and this single pivoting caliper is all the brakes we have. It must work properly. Hope this helps.

Gary