You should realize that pulling on the air levers a small amount only effects what happens when the throttle slide is pulled up past the bottom of the choke slide. I see several people, on starting a cold engine, insist it just needs a little bit of "choke" and then attempt to start with no or very little throttle.
As for the banging in the muffler, and if you are convinced that your idle circuit is clear ( A # 86 drill in that tiny hole in the jet block) then you need to either richen the pilot screw or look for air leaks. Did you seal the spigot joint when fitting the clip fit carbs, are the carb to head stubs sealed tight to the heads, they can get distorted over the years, are the exhaust nuts sealing the pipes at the head, and are the head to piston liner sealed with the correct clearances on the head joint. Min of 2 thou shallower for the counter bore in the head than the height of the liner above the muff.
I run NGK B6 series on both original mags and a newer BT-H so basically t he same heat range.
My B does pop a little now and then, especially on a cold motor but otherwise it behaves reasonably