...and for those of you "AFM is Gospel" bible-bashers, I challenge you to find anywhere in your AFM that this full-throttle auto-rich is even mentioned
Probably because its all covered in pilot course notes regarding the operation of float carburettors. Called the enrichment valve, or in the case of the Marvel-Schebler MA4 fitted to the average 172, an economiser as previously detailed by Oktas8. Called such by Marvel because it leans the mixture on reduction from full throttle.
None so blind as those that don't want to learn...
If you fly a normally aspirated, carburetted, fixed-pitch single, it'll take you about a minute at normal cruise settings to see where I'm coming from. Who knows, the few litres of fuel you save yourself by utilising a little knowledge, may one day be the difference...
I rest my case. Play on, kiddies.
A little more circumspection perhaps RadioSaigon? Just maybe there is something for you to learn, like getting out the books perhaps.