The original 32mm choke setting on the first Weber S/E engines caused some engines to stumble (flat spot) slightly around 1700-2000 rpm. This became worse as the engines got a few miles on them. The original settings for the Dellortos on the 907 engines when fitted to the Jensen Healey (first application) also showed this problem. Both were solved, with some slight loss of top-end BHP, by reducing the choke size. On the 907, some other jet changes were needed too. It seems to be a problem when moving from the slow-running jets onto the main jets and a careful or knowledgeable driver could probably drive through the flat-spot successfully. However, the choke reduction was a factory recommended change which I remember applying to several cars with complete success in terms of improving everyday driveability. Likewise with the JH.
1970 S4SE/1760cc big valve/SA-AX block, L2s, 45DCOEs, 1978 Jensen GT, 1962 AH Sprite, Alfa-Romeo 159, 1966 Bristol Bus, 1947 AEC Regal bus.