The 1406 isn't a bad carb at all once it's calibrated and they're stupid simple to work on. I didn't see you mention it, but since the carb is new, did you set the float levels on it? Off float levels and/or too high fuel pressure make Edelbrocks flood. For your step up springs, they should be half of what your vacuum level is, so the strongest springs in your case. The manual for the carb actually goes over tuning very well. Here's a good little tuning video from Jegs as well:
https://youtu.be/wR_AfQjyT-A