Trouble with a new Thermoquad Installation

Assuming no vacuum leak, it sounds like you need to adjust the choke pull off. Look up how much it should open from a "72" 340 carb and bend the linkage to get that gap between the choke tower and the choke. If that does not get it, you can start closing it up from there till you get it where you want. I use drill bits to measure the opening. This is trial and error so keep after it. You should be able to get it almost as good as EFI.