1988 Honda Civic Brake pedal very low

I recently replaced front pads ,calipers, rotors, & bleed the the system. And found out the brake pedal is almost to the floor. It only gets higher for about an inch after pumping the pedal 3 times. The master cyl. (rebuilt) was replaced few months ago with lifetime war. So I replaced the master cyl. again 2 days ago, and bleed the whole system again. Rear brakes were also replaced along with wheel cyl. few months ago. No leaks, everything looks good. Should I try again another master cyl.? Or could it be a bad brake booster. I hate to spend a part & find out that it did'nt solve the problem. I don't know what power bleeding is? Is this what what I need to do? If so, can you kindly tell me how to do it? Your advice will be very much appreciated.