Help with brakes please

[88Stanger]

So I just got the build to the point that brakes need to be done. Installed all new brakes lines, shoes, cylinders, conversion to feint disc, dot 4. So I have disc frint, new power booster, master cylinder and proportion valve. Got brakes bled as inetructed, front are great, very strong and solid, but the rear are acting strange. There is only a small about of pressure when bleeding them. The fronts - the pressure gushes out, the rear not so much, fluid comes out clean, but not under pressure like the front. Could a vend that may be kinked a bit cause this? Or?
Thanks for your time.