Forget the new carb, for now. Take the approx $500.00+ and spend some of that on a good timing light and dwell tach. With those two things, you don't really need a vac gauge, from my experiences. Then you can do things reliably and repeatedly, very accurately.
Will the engine start from cold and run on fast idle as it should? But then falters when the engine warms and the choke goes fully open? With the idle mixture screws set at their base setting, per the FSM?
Presuming the engine was running decently before you did the rebuild, what issues were you seeking to remedy with the carb rebuild? Did you readjust the base idle speed screw in the process?
Until you can get the meters and such to make the settings, turn the hot idle speed screw inward 1/4 turn at a time until the engien will run in gear. Then increase it by 1/8 turn until the transmission goes into gear without jerking and smoothly, PLUS off-idle response is good. All with the idle mixture screws adjusted 1.5 turns from gently, fully-seated, as a beginning setting.
In my earlier years, the first and least expensive diagnostic tool I bought was a vac gauge. According to everything I read was that it could tell you anything you wanted to know about an engine's adjustments and health. For an idle mixture adjustment tool, not so much, from my experiences. But in the middle 1960s, things like dwell tachs and timing lights were what real mechanics used and were expensive (to me). But by 1969, I had a Sears Craftsman timing light and 1970 a Micronta multi-range dwell tach. With those two items, I had much better results than I ever did with a vac gauge. In modern times, both of those will not work on modern, computerized engines, typically, so finding some used might be easy. Every so often
@halifaxhops has some for sale on here.
Sorry for getting a bit off track. There are some shadetree workarounds, but you do need the timing light and dwell tach to do a carb adjustment correctly with good results.
@Big_John's comments about fuel pump checking are good, too. One other manner to check for the fuel level in the float bowl is to remove one of the front lower float bowl screws and catch the gas which runs out until empty. If it looks like it is pretty much 3/4 of the total float bowl capacity, no issues with the fuel supply or float level. Make sure the gasket on the screw head is still there when done, too! Do this on a cold engine for better safety.
I'm presuming the engine has less than 100K miles on it, so the fuel pump pushrod should still be useable. Considering that I've put over 150K on 383s before I even knew wear on that part was something to worry about. BTAIM
After doing all of these things, getting the timing light and dwell tach, you can't get the engine to run off of fast idle, that's another situation unique to itself. An easy fix, too.
Keep us posted, please.
CBODY67
