The letters are the month of the year.
A B C D E F G H J K L M The letter I (eye) is not used.
The last number, say 6 7 8 9 0 is the year in the decade of production.
60's 70's 80's 90's
Sorta, kinda, gotta know the years the carbs were used in production, and manufactured.
Easy, peasy, once...