2 plug head dates back to when plugs were less effective outside their optimum, so you had one to start and cold running another for highway (speed) work.
its the right carb, why are you worried about the screw settings, is it running bad.
As far as it matters the one with the spring behind it sets the tick over speed by lifting the slide slightly, the other is the mixture screw (does precious little apart from the transition from idle to main jet. Its normally around 1.5 turns out.