Yeah, isn't the center screw an "additional air bypass" the demon version of drilling holes in throttle plates. this is used to increase air flow at idle so you can keep the transition circuit "out of play" at idle speeds?
Yep. And all new Demon mechanical secondary carbs come with them I believe??
My brother and I put a Mighty Demon on top of his built small block, and it took a little tuning to get it set up right. Once it was set though, it has been a fantastic carburator.
But back to the original question. You say it won't idle. Does that mean it stalls and dies at idle speed or does it race and not come back down to an idle???