Carter BBD confusion

Yes, they open, or a better description would be that the blades relax open. I don't think the throttle shuts by itself with any internal spring.

Your statement: "Upon installation i will have the throttle return spring on there and it will pull the throttle closed. if the spring ever happened to break or come off , the throttle would open to full throttle and make the car suddenly accelerate." is correct. However, the likelihood of that happening is pretty remote. If you want to be extra cautious, you should buy a new spring, or you could always rig up a second return spring in case the first one fails (an old racer's safety trick, but this will put extra tension on your accelerator cable).

I gotta fiddle with it tomorrow, if I spot this thread open afterwards, I get back at you.