I just hooked up the cowl induction on my 72 chevelle this weekend. I was just wondering why the flapper goes down when I step on the gas. Should it do this or should it go up when I step on the gas?

The flapper should most definately go up or "open". something must be hooked up backwards. It should be closed at an idle.

I have a vacume line running from the cowl vacume pod to the vacume advance for the carb., is this right? Should there be any type of check valve in that line?

Mine is tee'd off from the PCV valve.

I had it hooked up to my pcv valve but the was a constent vacume that held the flap down at all times.

Any one out there know what I am doing wrong?

Do you have all the components for the hood? There are many different parts to the system that all play a role in the operation of the door. If you just have the actuator connected to a manifold vacuum source, then the door will remain closed with the engine running. The door may open under hard acceleration when the manifold vacuum drops off, but will close back as vacuum builds. To operate as intended from the factory you need all the parts.

You say the flap goes down when you step on the gas, which position is it in when the car is off, or just idling?

My '72 has factory cowl induction, flap is spring loaded to stay up in low/no vacuum situations, when idling/normal driving the vacuum pulls the flap down, and when you step on it naturally vacuum drops and the spring overcomes it and pulls it up.

After reading your post again, It sounds like you have it connected to a ported vacuum source. That would leave the door open and close it as the throttle is opened. Not exactly what you want. The valve in the line is called a flow control valve and will not help you without all the other parts. With the system operating properly, it slows down the movement of the door.