HS1 SU Carburettor

[Bob Culver]

Thanks Tony, but because of the sparse markings and interchange of parts the full picture is still vague. I suspect carbs  without springs contd after 1948 and carbs without the diagonal rib after 1950. Unless have side by side or otherwise familiar with all, it is difficult to know which piston assembly have. Prior 1937 was there no flange for air cleaner?. And were mount holes horizontal until 1937? Was 1 1/8 available prior 1937?
The 1 1/8 1938-1950s with dashpot and ex Series E and Morris Minor is/was common and seems to suit Sevens well.