I am looking at purchasing a 74' R90, unknown mileage, very good driver condition.
I am concerned about the disc brake though. The owner said the master cylinder has been rebuilt. The front brake does not stop the bike like I believe a disc brake should. It feels like an old drum brake. No modulation, no grab, just a hard wood like feel to the brake lever. I cannot get it to lock the front wheel up no matter how hard I try.

What is the collective consensus about this? I am not opposed to rebuilding or replacing the master cylinder and or caliper if need be, I just would like to know if this brake is normal or should the disc brake be more like the modern day disc brakes? ...yes I know this is a 1974 single disc and will not be like a 2013 system.

Thank you in advance.