Air from the air filter and gas from the "gasplant" approach the motor in their own equal tubes.
In the airtube there is a "perfectly" symmetrical and tight airflap, immune to "flowpower!
A membrane with ~80% of its diameter reinforced with (aluminium plates)
making a light and stable "piston" to control the airflap.
The membrane material shall exercise NO "spring" action on the movement.
The airflap has to do full movement between open and closed within the full movement of the membrane "piston". No favorite position given.
The ONLY aim with the membrane is to keep the air (under)pressure on the same level as the arriving gaspressure, when there is some gasflow.
The membrane has nothing to do with DISPENSING air/gas in the right proportion! Only delivering air and gas at the same pressure for LATER DISPENSING by other means.
"By other means" is i.e. a twin throat carburettor body with the acceleration nozzles removed = straight throats.
If throat 1 and throat 2 have different closing angles, get troat 1 flaps from two identical carburettors.
Then gang them with a "paralellogram-beam", so their movements stay identical!
That takes care of IDENTICAL DISPENSING of gas and air.
The same can be applied to a 4-throat carburettor with identical throats.
Now, at last follows "gasmixing"! It has to be carried out with FULL SYMMETRY IN ALL DETAILS, or otherwise you will end up with the same misery as DJ in his pickup!
When the spiral mixing is done, then there is no more problem affecting the dispensing result...