A selector valve and shutter mechanism for use with a gas burner unit is disclosed. The valve includes a pilot gas manifold which is in communication with two pilot flames and associated ODS for two different kinds of gas fuel. The shutter mechanism opens or closes an opening to a burner mixing chamber to thereby adjust the flow of air into the mixing chamber depending on the fuel selected, and preferably is in the form of a sleeve that in one approach is rotatably mounted on a part of the burner mixing chamber, with a part of the sleeve covering the mixing chamber opening in one orientation and opening it to airflow in another orientation. A first gear is mounted on the sleeve which is engageable with a second gear mounted on part of the valve which is rotatable to one position or another depending on the gas fuel selected, the sleeve thereby adjusting the airflow to the mixing chamber in response to the valve position. In another approach, the cover moves linearly along the burner tube between orientations. A novel selector mechanism having a manifold for gas flows and a plate-like element to adjust the manifold is also disclosed.