-SG- ... was noteworthy for two reasons - first, in the autumn, the Great Depression affected world wide stocks and shares and caused unemployment problems which lasted for several years. Sales of Norton machines were affected - such that, for instance, the despatch books show many machines dated 1930 which were not despatched to a dealer until 1931 or even 1932.
Secondly, 1929 marked the establishment of Amalgamated Carburetters, used by virtually the entire UK motorcycle industry from then on. The only exceptions I can think of are Villiers, who made their own carburetters, and Bowden Carbs. which were available to those who wanted to use them. My 1930 Model 18 had been fitted with one before I bought it in 1956 and I must say it worked very well. Incidentally, I no longer have it!
The first Amal carbs. used a cast brass float chamber with a relatively long float needle (3.405") but this seems to have been changed quite early on to a shorter type (part number 14/024 - length 2.950") following a change to the position of the needle seat. This shorter needle was seemingly used in all Amal float chambers fitted by Nortons throughout the thirties.
The scan attached shows the needle seat positions.