Be sure master cylinder cover is loose before bleeding with a catch rag under it. The cover vent bellow may be old and stiff. The system is not vent to external air, just with the bellow..if it's like the newer bikes.

 

In an older brake system ., rust in the bleeders and fine dirt clogging the tiny holes in the master cylinders are things to deal with.
Replace the old bleeder screws with new or speed bleeders.
Ensure a good flow of fluid escapes when the bleeder screw is removed as rust creaps into the tapped hole the bleeder screws into also.
As for dirt in the tiny orifices in the master cylinders , i drain or pump out the fluid and use a vacume with a cobbled together attachment on the hose to vacume the hell out of these little holes.
You will see just how much crap can accumulate in the bottom of these master cylinders.
One other odd thing that i have seen is a older brake hose that has deteriorated on the inside but looks ok on the outside. A piece of the inside rubber hose flecks off and becomes a one way flap valve that allows flow in one direction only . I have extra grey hair figuring that one out , what a pita that was !

 

Use a syringe and push the fluid in through the bleed nipple...it's the most reliable way.

 

Update: I pulled the master cylinder apart again and found the small hole into the cylinder from the hole where the reservoir line goes in was clogged and would not let the fluid come into the cylinder. I cleaned it with a welding tip cleaner and put it back together and filled the master cylinder up with fluid and put a very small amount of fluid in the hole that is supplied by the reservoir and pumped the piston by hand, it took a few times but eventually the fluid ran into the cylinder from the hole where the reservoir attached. I put it all together and bled it the old fashioned way until I got fluid from the caliper then hooked the vacuum bleeder to it and pulled it through. I got good pedal and will try it out as soon as the weather is a little nicer. Thanks for all the suggestions.

 

Glad you got it figured out.