Progress report. Today I've been working on the "twin flaps" aka the woodgas throttle. They must be distinct yet identical passages, one for air, one for gas. I'm using a Ford throttle body from a 90's F-series truck:
First I plugged off the idle passageways. JB Weld in the center area:
A rivet, to close up a hole in the throttle plate:
Now for the output side. Max says it needs to swirl some so it mixes together, so I've made some deflectors to get it spinning:
Then I need to merge the gas and air:
And then a fitting for 3" PVC, something I can clamp a Fernco on to:
I have tested the airflow with a shopvac, there is lots of swirling happening. It will spin a pencil around pretty quick. I may at some point add an inline swirler, but I'm going to start with it as-is, I think it'll work fine.