I have the weber book, so I understand that there is little rhyme or reason to how weber named them.

Referring to weber DG/FV carbs:

if F6 is rich What is F66?

my book doesn't even show such a emulsion tube.

you probably know already but it's not juat a matter of rich or lean but how much vacum required to lift the fuel (gas) to the holes in the tubes
never seen an f66

They're complicated beasts, It's a combination of the inside diameter, the outside diameter and contours and the sizes and arrangement of the holes.

the f66 is listed in the book, but it's not mentioned in he rich - lean table f6 s the richest they list.