Brake Bleed and lost of air

[btgrande]

I have a ´69 Short Stepside, I installed a comple disc brake kit from ECE (front and rear), and a complete stainless steal brake line kit from inline tubes.
I have properly bench bleed the master cylinder, drilled a new hole on the brake pedal, 1" lower than the original hole, as this was a manual brake before. Checked that the rod length is correct from the pedal. But air is keep coming all the time. There is no leak in the system... What can it be?
Enclosed is pictures of master cylinder and proportion valve.

Regard, Bjorn Tore