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Yes, the B-17 mixture controls are 'reversed' from what is considered standard. And, this can be a negative transfer in the airplane, particularly during an emergency. One must remain deliberate and focused. Particularly, when flying multiple types.
Full forward position is ICO, ....as we move aft...Auto Lean, Auto Rich, and Emergency Rich (the full aft position). ER was removed circa '47, as per a Bendix Service Bulletin that was issued. So, we simply have Idle Cut Off, AL, and AR, positions these days.
Pressure Carbs, essentially all function the same with some nuances. There is no 'ground lean' in the manner in which you refer to it.
After start, the mixtures may be left in either the AL or AR position, as it makes no difference. I usually move to the AL position upon starting , just in case I perceive an engine may be overly primed a bit, as its easier to 'stroke' the mixture control, in and out of ICO rapidly, to clean up the engine for a normal fuel/air ratio for smooth engine idle. This is just a technique.
To keep it most simple, the Pressure Carb's function is thru air pressure metering, and fuel metering. And, without sufficient differential pressures, the carburetors air and fuel chambers do not function. This occurs when the throttle blades are below about 10 degrees with respect to the closed position stops. In this arena of operation, fuel metering is rendered by an Idle Mixture Valve. This is adjustable and set at a desirable fuel/air ratio out at the carb.
At higher elevation airports , say above 4 or 5 K, it may be necessary to position the mixtures between Auto Lean and Idle Cut Off, (moving the brass mixture control plates) since the Idle Mixture setting may be overly rich, causing the powerplants to load up and quit.
Hope that helps.....
Bob
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