Superbly written piece of purple prose Sir! I salute you!
Glad to hear you are pleased with your student's progress
From what I understand it's a balancing act
Pretty much. From my point of view getting it very slightly on the lean side of stoichiometric is what I'd aim for - that increases CO and IIRC NOx. That certainly reduces carbon and leaves less of it in the oil and the exhaust pipe - when you look at the end of the tailpipe it should be white. The burn temperature is higher and if it's too lean it'll start to burn out exhaust valves so it needs to be lean enough to bring the CO to the point where it's
just under the CO limit for the MOT test - which varies by year and by model, and the cooling system needs to be clean.
When setting up with the air cleaner off, slightly blocking the air intake should tend to stall the engine and tickover is 'fragile' in that it's easy to stall when pulling away with very little throttle, but mpg should be very good.
