People get confused with the word "leaner"... or "leaner mixture"...
This term is meant to mean the ...fuel to air mixture... NOT the oil to gas mixture.
It is adjusted "leaner" or "richer" by a couple diff. methods
Bigger (richer) or smaller (leaner) main jet.
Raising (richer) or lowering (leaning) the needle on a slide type carb
Turning the idle mixture screw in (richer) or out (leaner) for idle running.
So when I said his mixture needs to go LEANER ..I was NOT saying to put less oil in... I meant to put in a smaller main jet.. (less fuel to go with the air)