The grill that you have does not have the venturi tube with the screw for
adjustment. A yellow flame can be caused by the following.
A blockage in the venturi tube or orifice. Burner rusted out. The venturi
tube may be misaligned, readjust over orifice.
A yellow flame that is one inch tall is acceptable as long as there is no
soot deposits or carbon. Some grills that have been used for a while
sometimes begin to have a yellow flame.