Flutter below 2k rpm

I am somewhat familiar with plug reading but its kind of an art .
There are about 1000 miles on the plugs.
As far as running lean my Wideband show me between 12.5 and 15.5 at the leanest. Most low speed cruising is around 13.5

The QF 750 VS I was running had it so rich I had to wipe down the rear bumper !