All the 750cc Norton Commando’s and the earlier 850cc models were fitted with a more-or-less rectangular air filter with two shaped rubber hose connectors from carbs to the filter front plate.
Restorers will know what a difficult job it is to assemble the carbs, connecting hoses and filter between engine and frame, and then afterwards how difficult it is just to change a filter element. Only in 1974 with the MK2A 850’s, did Norton’s change to a much simpler and easy-to-get-at pad type air filter which could be changed in minutes.
Setting up and tuning carburetors with BSA or Triumph twins with their dual easy-removable “pancake” air filters was easy, enabling one to get into both carb intakes to “finger feel,” or the other trick of inserting two same-sized drill bits shank first under the slide cut-away’s, and watch to see them dip evenly as you tweak the throttle.
Final carb setting is not easy on a Commando because it is NOT a five minute job to get into the carb intakes to adjust the all-important simultaneous slide lift. Much easier way is to use two pieces of straight wire inserted through the top cap usually blanked off holes for choke slide, and watch the tips rise together. Easer to see if you glue a piece of white board on top of the wire. This all assuming of course that you have as most British bike owners of Amal carbed bikes have done, and discarded the choke mechanism, and again what many Commando owners have done and replaced the original air filter with K&N cone filters. If my carbs still had choke slides I would have drilled small holes in the carb tops to take the wire, then blocked them up again, rather than battle with taking that #@?!! air filter off and then on again!