912 ULS running rich

I'm somewhat puzzled as to why my 912 ULS is running rich, on warmup, it runs rough between 2000-2400 rpm, after flying, its usually fairly smooth at lower rpm.  I checked the plugs yesterday and they are black and somewhat glossy.  I'm able to get pretty decent manifold air pressure.  I have an airmaster prop.  Field elevation is 2,000msl, on takeoff at 5800 rpm i'm achieving 27" MAP and at cruise at 5000rpm i'm achieving anywhere from 24-26" MAP depending on density altitude.  Here are a few pics of my plugs.  I have been debating on moving the circlip to the #2 spot... thoughts?