Holly 1920 carburetor adjustments?

There is no set number of turns for the mixture screw — that's not how this works. The correct way of adjusting the idle mixture is described below the carb operation and repair manuals and links to training movies and carb repair/modification threads in this thread.

That said, 5 turns out suggests there's a problem with your carb -- trash (dirt) in in the idle circuit, for example. Try the technique described here.