Gas range top burner - fuel line blocked between valve and burner orifice
I was able to clear the blockage.  I considered a number of different cleaners to see what I might use.  All of them said don't use on aluminum.  The gas line is aluminum.  I settled on dawn dish detergent in water.  Soaked it overnight from the burner side.  Applied compressed air to the valve side of the gas line and it eventually blew out the obstruction.