we must be very lucky, only ever used unleaded in the time we have owned it, never had black soot, no smell, cooks well, never had to clean jets etc. very easy to use, very economical too
We love our coleman - a lot of the initial decision was down to room in the car...
I do need to take ours apart for the first time (we've had it 6 or 7 years) over this winter to clean it up, but I've never really had a problem (one nut needed a bit of a tighten, but that's all).
I use unleaded and whilst it can create a bit of soot on the bottom of the pan sometimes, that hasn't ever really bothered me.