KDX's do rattle at idle, almost like a diesel. My 05 doesn't smoke excessively, I would get away from the chainsaw oil and try something for the bike for starters. Does it have a lot of wear? Could be time to do the top end, freshen up the rings. The idel could be an idle adjustment, tough to say without seeing/hearing it.
32:1 I believe is the stock mixture, pick up a ratio rite and you'll love it!
Great bike BTW, I don't think you can beat it in the woods without spending $8K or so on an orange 300.
Trees are like magnets, if you look at one too hard you'll probably hit it.
I miss my 01, the silver was fastest!
08 Concours....as close to silver as I could get!