yes, the Demon is and the Eddy Thunder series are copying the TQ air door, which was very successful if tuned properly. Also, check at some point check and see if you have any adjustment on how far that air door comes open, that's key as well. I think the Demon carbs will work great once tuned.
Yes the air door is spring loaded and you can put more or less tension on the spring. Most are saying to put more tension on the spring and not let it open. I may need much more tension..
I'm pretty sure the secondary door is spring loaded. Here's a full-out picture you can see the spring wrapped around the rod...
