My cover doesn't leak, but I know that when I strip it down the KIPS is always covered in thin black oil, quite wet in fact.
Inspite of that, they don't appear to carbon up very much at all, and so I try not to let it bother me.
I run a good quality synthetic oil at between 32 & 40 : 1 (32:1 for racing and 40:1 for trail riding). My jetting is fine so I figure it must be normal to have this oil on the KIPS. It's not like it drips from the pipe or anything...
Cheers