Need tuning help with 4100 Carburetor

[Gary’s 67]

I’m using an Autolite 4100 on my 67 Mustang coupe with a 302 engine and mild 268 cam. I can’t get enough idle rpms to run without cranking on the idle stop screw and getting into the transition circuit of the carburetor that makes the idle mixture screws useless. I’ve got the initial timing set to 13 degrees. I don’t know what the correct fix for this would be. Any help would be appreciated

 

[Noobz347]

Is this a new or used carb?

 

[Gary’s 67]

Well it is used but I recently rebuilt it, everything is adjusted correctly, proper wet float level checked, 1.08 Venturi, proper boosters, checked the power valve, just can’t get enough air flow without opening transition slots