I have a 30 over 360 with stock heads, small Edelbrock performer cam, and 625 AFB carburetor. It runs pretty good when driving, but will barely idle, it drops from 750 RPM to 400 when I drop it into gear, and barely stays running. There are some days it runs fine, then sometime during the drive it starts idling bad again. I have changed ignition box, coil, plug wires, distributor, cap and rotor, I have even swapped carburetors, still the same. My initial timing is 20 degrees (that is where it likes it), I think it may be a vacuum leak, but i cant find it, i have blocked every vacuum port on the carb, and sprayed around whole base with water, no change. It is taking a lot of fuel to run, my idle mixture screws are almost all out, and when i partially choke it, it seems to run a little better. I am about to change intakes and see if that helps, any suggestion are appreciated.