Hi I had the same problem with a JTX250, when i removed the brake line from the master cylinder and blocked the hole with my thumb it had pressure straight away but as soon as i put the brake line back on there was nothing. I tried forcing fluid from the caliper to the master cylinder to remove any trapped air and then into the reservoir bottle, bleeding it at the master cylinder and at the caliper brake line connection and the nipple and eventually i got it working but unfortuanately i dont know how, all i can suggest is keep trying (it took about 6 hours in total).