At the top end of each valve, there is a tiny gas opening known as an orifice. The gas exits the orifice and enters a venturi where it mixes with air coming in from the side air shutter. The proper mixture of air and gas produces a clean blue flame at the burner.
Make sure the valve orifice on the control panel aligns with the burner venturi tube correctly. The orifice should fit into the venturi tube 1/4″ to 1/2″ as shown below.