Carb Help!!!

I'm at my wits end with a carb for my motor. Im running a mild 340 and initally had an 800 cfm Edelbrock on it. I know, way to big. I picked up a used Edelbrock 600 CFM , bolted it on and it was pouring fuel out of it so i decided to "attempt" a rebuild. Took the carb apart, cleaned everything, all new gaskets, floats etc. Buttoned it all back up and bolted it on.No leaks but I cannot keep the thing running. Its almost like someone is throwing a switch and cutting the fuel off. If i turn the ide screw all the way in ,it will fire up and idle at about 2700 RPM and as soon as I touch the idle screw and back it off it immediately dies. If I start it and keep the engine rev'd it will stay running for 10 seconds or so and then it cuts off. I adjusted the floats and from what I could tell they were really close to the 7/16 but maybe not. I am not a carb guy and thought instead of buying a new one or paying someone I could try and learn something but I am kicking and screaming. Any help would be appreciated. Thanks!