Lean fuel "knob"
I was checking out a 1973 Cessna A150 Aerobat, and noticed that directly beneath the mixture control knob, is a smaller square knob (which looks just like the carb heat knob but smaller) labelled "Fuel lean..." something something not quite legible.
Can't find anything on the Owners Manual on that knob.
Any ideas?
p/s Apologies can't post a picture, did not have a camera when I was at the aircraft...