I put a 600 cfm holley on my 65 289 car and was working ok after I rebuilt it with a 5.0 Power valve instead of the 6.5 like it was originally put in it. I thought sticking a 6.5 in it may make its throttle a little more responsive. The result was a car that will run allright but fuel will gurgle out of the top vent stem of the primary bowl. we think the timing is a little off and the carb is by no means tuned perfectly, with the 5.0 power valve it ran ok but the exaust would sound a little bit off, it would make tiny pops and didnt have a smooth note to it. Should I stick old 5.0 back in or replace the 6.5? or should I try and set the timing better?

Also I pulled the adjustment needle as far out as possible and it still flooded, which is shouldnt do. The front fuel sight hole would gush out gass but the rear sight hole would sit with gas barley trickeling out if you push on the front end like it should.

 

You need to have the spark and cam timing,fuel pressure,and valve lashall set to the proper spec's before you can properly tune a carburetor.This makes the process a lot easier by eliminating variables that always cause you to yank your hair out in handfulls.A vacuum guage can go a long way in helping you figure out stalling/hesitation problems.
I don't have much experience with these carburetors but you might try looking at the Holley website for some help.
http://www.holley.com/division/Holley.asp

If this carb has run on the car in the past but for some reason it won't run now you should restore the carb to it's original condition and go from there.I would think by the symptoms you describe the fuel pressure is too high or the floats are set too high.This can cause you to install smaller jets than what is optimum to get the mixture right and either the engine won't idle very well or lean out at high rpm.
Get the engine running smoothly on the primary circuits before you worry about the secondary circuits.Change only one thing at a time so you can see the effect the change has on the engine.Changing several things at once will have you chasing gremlins forever.