Carb replacement

Hi to all. I am replacing the carburetor on a Briggs and Stratton 656cc twin cylinder engine. The new carb has a welch plug where the idle mixture valve is. Should this plug be removed or is it there because the carb is not to be tampered with?

That could be covering an internal adjustment screw or could be a cover for a fixed jet setup. In either case don't worry about it. If the carb is running fine no reason to mess with it.