[RichardJ]

>>should be pedal be harder/more firm with the booster set up when the motor is running?<<

Pump the pedal a couple of times and HOLD. You should have a very high, firm pedal.

Start the engine. As vacuum builds, your foot and pedal will drop.

The booster is designed to hold vacuum for 3 applications of the pedal. If the engine dies while driving, the booster should hold plenty of vacuum to give vacuum assist in order for you to get to the side of the road.

Turn the engine off. Apply the brakes 3 times. The pedal should be higher and firmer after each successive application.