Next Step???

[Orange72ChevyC10]

Ok first off thanks for all the help in my last post, as a recap, I wasn't getting spark and there was no resistance wire on my truck wire harness. Long story short I have installed an HEI (getting full 12v) and have been able to get the truck started, kinda!!!

Here's my question: What to diagnose next? Here is what I can confirm, the quadrajet is pumping fuel (it has not been rebuilt, however I have cleaned it as much as possible). When I crank the motor it will fire and run smoothly if I give it approx. 30% throttle. After that I can manually open and close the air doors on the carb, step back into the truck and crank the truck without throttle and it will idle smooth from 15-45 seconds...it then becomes a weak idle then dies.

Thoughts on where to begin?

This is a factory 350 with zero mods, I am going to confirm that the vacuum lines are all connected. It is still the original brake booster as well.

Jason