90 prizm proportioning valve

I have an 90 prizm which I just bought and it had a blown RF brake hose...I replaced it....now I know the front port on the master cylinder controls RF and LR brakes....my problem is when I bleed RF brake I get a little bit of fluid out but when I do LR I get nothing out of it...does this sound like a proportioning valve...does anybody know how to fix this problem short of replacing valve....also the other 2 brakes bleed fine and I can bleed both lines off the master cylinder....Thanx in advance