Not enough air does seem to be the cause of the soot and yellow flame. This is indeed a cheap burner. As such, the problem may be with something blocking the flow of air. Take off the shutter valve that controls the air flow and look inside. You will probably see a bunch of casting slag left over from manufacturing. You can knock most of that out with a screwdriver and that should improve the flow. Burners that have been stored unused for quite a while develop similar problems, only the blockage is caused by spiders or other bugs taking up residence in there. Clean out the burner and the problem should be solved.
Wayne
