From Amal (link) website

Full Set Part Number: ACK334
Description: N/A
Make: Triumph
Model: T120C (Johnson Motors)
Engine Size: 649cc O.H.V.
Carb Type: 389 Monobloc
Year: 1963 to 1967
Number of Carbs: 1
Needle Position: 2
Internal Bore: 1 3/16in