I was doing a brake bleed but it seems like there is a lot of air in the system even doing the regular 2 person bleed.

Is it the proportioning valve that is preventing a complete bleed? If so, how do I bleed the proportioning valve and maybe a gravity bleed to ensure all the air is out of the system. I've already got the proportioning valve tool. The entire time the M/C was kept between min and max.