Maybe the idle circuits have changed, but rule of thumb on idle mixture screws for a Holley were start at 3/4 turn out, then adjust from there. Spent decades starting there and had much success. (yes, did it for a living 40+ yrs)
If you adjust the idle screw don’t forget to go back and check the accelerator pump as changing the idle screw will affect the tightness if looseness of the accelerator pump linkage.
If it's coming out the vent tube either your floats are adjusted way too high, your needle is stuck open (first thing I do when I see an overflow is smack the float bowl with the back of a screwdriver. Will usually free up a stuck open needle) or your fuel pressure is too high. If it's coming out the float adjustment screw you either don't have it tight enough or your gaskets are bad.
Thank you for answering buddy I greatly appreciate it is coming out of the tube that's sticks out of top of carburetor....the front is primary an back is secondary right? It's hard for me to explain like this lol.. I've taken both of the check valves out an they seem ok... it's my dad's 64 Impala I will try what u have mentioned an will get back with you thanks
