Soft brake pedal Rover 825?

Just replaced the master cylinder on Rover 825 Coupe 1996. Replacement cylinder came from car with good brake pedal. Have bled system using miti-vac vacuum system, and by conventional pedal pumping. System has pressure and pedal feel is better than previous master cylinder (which had failed seals) but pedal is still poor with too much travel. Still feels like air in the system. There are no leaks, clamping the flexis off makes little difference, there is no pad knock-off due to wheel bearing play. Has anyone had this problem? Any special method needed bleeding the brakes?