#4 is the base carb on a 1200, all others synch off it. Turn the base idle screw in to get the vacuum to come down, the idle will go up, then start adjusting the others to match #4.
I didn't see all the responses when I said that I'd be quitting for the night. Sorry about that. I'll work my way through them now.
I got that #4 is the base carb. As such, I thought #4 has no adjustment so I don't know what you mean by "base idle screw." Here's what I know/have worked with - four idle mixture screws, three carburetor adjusting screws (one screw each on carb 1, carb 2 and carb 3), and the throttle stop screw.