Hot Rods 32 5 window build Brake ?

I am using a Mustang II brake system front disc drum rear dual booster and master cylinder. With out the engine running i have a good pedal with 3/4 of an inch depression prior to engagement of the brakes. I have checked the ratio its 6-1 ,adjusted the plunger pin between the booster and the master. With the engine running i have brakes but there is very little resistance on the pedal. Its not spongy but it just goes down and it will lock the wheels readily.i would like to have some resistance on the pedal. Any suggestions as to what is wrong ?

 

if it is power unit there is not much resistance with motor running tom