The two carburetors are connected downstream by a balance tube whose purpose is to roughly equalize the manifold pressure seen by the two carbs. On the 912 the system manifold pressure of the twin carburetors is sampled through this balance tube at a single point.
David Heal - Windsor, CA (near Santa Rosa)
EAA #23982 (circa 1965) - EAA Technical Counselor and Flight Advisor; CFI - A&I
RV-12 E-LSA #120496 (SV w/ AP and ADS-B 2020) - N124DH flying since March 2014 - 1,060+ hours (as of Aug 2021)!
through June 2022.