The Magnum 108 carb has a 11.5mm bore.

With the old style Magnum 91 spring steel bushing, it has a 9.5mm bore

The bore on the Super Tiger carb is 8.75mm but it has a flat sided narrow spray bar that makes it effectively larger.

If your Super Tiger 90 has a round sided spray bar, it is the carb for the 40, 45, 51 engines.

The only difference in the big and small Super Tiger carbs is the spray bar.