I am lost about any diaphragm functions with so far unknown modifications.
One can use the gasoline-air throttle body for air, making use of the flap position reader and letting in woodgas below this throttle body through a Y or T piece! Preferably spiralling.
The woogdas throttle body must however be identical by geometry with the gasoline-air throttlebody.
Then they are ganged together when using woodgas, separated when using extencively gasoline.
The gas-side of the membrane connected just ahead of the woodgas throttle, the air-side just ahead of the gsoline-air
Still further ahead of the air sampling point comes the arriving pressure balancing flap operated by the membrane.
This flap can be 1m or more ahead of the air sampling point and the gasoline-air throttle-body!
If the gasoline "delivery" is sensitive for the balancing "vacuum", made by the membrane-operated flap, then the gasoline must be cut-off when driving on woodgas.
This makes a simultaneous two-fuel drive hard to manage...