The majority of sources I have read over the years use 65% as the
maximum power at which unrestricted leaning will not burn the valves
or detonate.. It is the number I use, though with my low compression
engine I probably could go as high as 75%, but why take a chance...
And with a carb I lean aggressively... If I lean too much the engine
will start to shake like a wet dog from uneven power pulses, a smidgen
more lean and it simply shuts down...

denny