Brakes again

[katbloke]

Ok guys went to the garage today and fitted a new master cylinder, bled all four corners and everything felt fine, went for a run and bang only have resistance at the very bottom of the pedal took it back rebled same thing has anyone had this b4 and could give me some pointers cheers, im thinking poss knackered bias valve but need someone more used to williams brakes than me.

Cheers Katbloke.