As the good Doc says,,,with twin carbs, it`s not a matter of adding them together,
they still only get sucked through(for want of a better description) by each cylinder seperately/alternately,,,each suck (so to speak) still only comes through one carb,,,so,,,if piston #4 goes down, it sucks through the single rear 1&1/4" carb...ok?...then #3 piston goes down & sucks against the same rear carb,,, a single 1&1/4"-----then #1 piston goes down & sucks agains it`s front carb,,,a sngle 1&1/4"---then #2 piston goes down & pulls against the same carb 1&1/4" twin carbs but basically work as 2 singles.
so as you can see,,,whether there are 2 carbs in a twin set up, or a single carb, the engine & all of it`s cyls , still only sees the avaliability of the one carb,,,
lots of going down & sucking & pulling,,,but,,,at the end of the day, it really does come down to "SIZE DOES MATTER"
the biggest difference between the twin & single carb set ups is a matter of the flow/restrictions in the 2 different styles of manifolds,,,twin will allways outdo a single simply because of the manifold is far less restrictive (flows more easilly) & also creats a far better, more even distribution of gasses between all 4 cyls,,,single carb manifolds tend to bias the cyls to a point where the 2 centre cyls run richer than the outer 2 cyls,,,YuKKY, but typically acceptable for road use.
I run a single 2" SU on the 1510cc roady donk
twin 1&3/4" on the 1415cc race donk
Full Autronic engine management & 2" trottle body being pushed through by a hair drier on the Twin cam 16v Bimmer headed beast (nearing completion)
