I am restoring a '71 Chevelle with a 454. I just got the engine back in the car and I've added several parts to get the cowl induction hood working again. Now, when I start the engine, the vacuum modulator closes the flapper door. Is that right? I thought it was supposed to close when you step on the gas. It's like it gets too much vacuum when it's idling. Please help - this is the first Chevelle I've owned with cowl induction.