Sooty plug options ?

My 0320 carb engine shows sooty plugs upon removal. Yet the electrode appears brown. I always lean to rough, then smooth when flying. My idle cut-off rpm rise is only about 20-30 RPM rise. I made it more rich to avoid possible approach issue in winter. Is the idle soot a non issue ? Any thoughts/suggestions ? Oh' BTW, I use no ethanol mogas.

Lycoming says...

I came across Lycoming's comments on spark plug interpretaton just last night in http://www.aerovalley.org/data/Manuals/Lycoming/Lycoming%20KEY%20REPRINTS.pdf

See pg 85.


Bo