sometimes taking the master apart and cleaning it will make it work better, you gotta think, these bikes are 25 years old and there is always some kind of build up in there.

when you take cover off the master look down inside of it you will see a black rubber boot that has some slots in it.
take that out, a small pick can get it out, it just slides back in when done. this will let fluid drop in the chamber faster, keep working the lever. if you want spray some brake fluid cleaner in there first and work master a bunch of times, holding your finger over the hole. you will feel psi build up and crap start to come out of it. when i did this fluid was black and had white corosion come out of it, flush it with fluid before you hook lines back up. and make sure banjo bolt has a clear passage, blow a air gun through it. if you have one. blow out master to if you can. but a bad rubber o-ring will not let master build up enough psi to work brakes good. i think there are 2 o-rings maybe 3 in the master. you can take it apart and clean it, stuff a clean rag in hole and stick a screw driver in it and turn it a few time to clean it out.