I agree, adjust the air intake tube. Soot indicates to me that the flame is running rich rather than lean. This means that your orifice is not plugged, but the air intake may be.
I know that a spider had made a nest inside of my air tube and plugged it up completely.
You can take the tube off and blast it out with compressed air. Once you know it's clean re-install it and light
Adjust the air intake so that the flame is mostly blue, with a slight roar to it. Not a loud one that you can hear from inside the trailer, but not quite silent either.