Hi there, I believe that the burner you are having a problem with, needs the inside of it cleaned, probably has alot of dust inside, or some material is in/on the orifice where the gas enters, you could also have an alignment problem with the orifice, causing a disturbance in the flow of the gas/air mixture. In addition it sounds like you may have a gas pressure problem, you should contact your gas supplier to have it checked, or call your local service company.
Hope that helps, and thank you.

The buRner that puts out soot need to be adjusted down a bit!