I guess I'm mechanically gifted... I usually pull 'em apart making mental notes of how it goes back together... Then I can reassemble them 3 week later without a book or pictures even. I've done 4 hitachi's (motorcycles), 2 holleys, a Carter, a Solex, but no SU's or ZS's yet... But I would feel confident in "doing" them though.
I work the same way on engines... Yes I've documented my Toyota teardown, but I may not even look at the pics on reassembly - to include the vacuum hoses. I will look up torque values for certain bolts though, but other than that, my Haynes manual will probably not be cracked open.
I've always been like that... If I can take it apart, I'll remember how it goes back together.
I built tons of model cars over the years, and watched and helped my dad rebuild tons of cars and engines, and carbs... I'm sure that helps. He used to consult the BIGGGG Chiltons book though - and frequently.