No idea with vacuum, car has been sitting for about a year, being driven minimal 2 years before that. Dont exactly know how old the gas is but I remember putting stabil storage in before storing away for every winter. I am running an inline fuel filter between the pump and carb, along with the brass filter in the inlet. Couldnt tell you the age of the carb, buddy gave me the thing after running into an issue with a q-jet while on the run stand. Its open headers right now but it doesnt smell like fuel, just exhaust.
Try starting it up, put hand over carb horn, if it revs go up its a vacuum leak. Or spray carb cleaner around bottom of carb, if leaking revs will go up.
If you can get a gauge an put it on a vacuum outlet should be 16 or up, depends on camshaft.
But honestly to me when l first read this l thought flood has issues that's why it's dripping fuel even after you shut it off because there is still limited pressure in the line until system equalizes. It's a Holley so there should be a top adjustment screw for the float. You can adjust it with car off but better when car is running threw the side site, adjust float until no more fuel comes out site hole if it's not the glass plug, if glass adjust it to the bottom of glass. This should atleast fix float issue enough to keep it running unless float has a hole. If you think float is issue, take bowl off and float and put float in a cup of gas and see if it floats.
If floats are ok then adjust side screws on side blocks to 1 3/4 to get it started, then with a pressure gauge attach to a vacuum line and get the vacuum to it's highest point by adjusting block screws.
If you can't get it to run trying any of this there is dirt stuck somewhere in the carb, most likely between needle and seat, an you might want to check that before you do anything else.
If you have a factory fuel pump it should work just fine with that carb, put you could put a regulator inline to check, cause there is no return line on that Holley, so carb has to eat what the pump gives.
Does carb backfire? Bad gas or dirt.
Not sure how long fuel stabilizer last, but a year is alone time.
Anyways l'm out of wind now so l hope that helps. The only other thing it might be is the pump in the carb and the adjustment that it might require. But that's another story, !
