chamber 46 and the velocity of fuel air flow through flame ports 66 again this flame retention device design can only be determined by prior experimentation to match the aerodynamic structure of the retention device for a particular appliance aerodynamics also it is not precisely known for sure why the flared portion 56 of passageway 36 and the flared portions 60a and 60b of carry over ports 58a and 58b respectively operate to provide the advantageous results obtained however it is thought that the flared portions aerodynamically configure a portion of the secondary combustion air away from the flame retention ports to in part protect the combustion flames emanating therefrom thereby producing a stable flame front at the flared ports however it should be understood that the aerodynamics involved with regard to the primary combustion air being aspirated through passageway 36 and the secondary combustion air being induced by blower 14 around the burner body present a very complicated aerodynamic problem which cannot be fully understood at this time it can be said that the flared design of burner passageway 36 and the continuous flare of carry over ports 58a 58b in cooperation with the unique flame retention device tuning method disclosed has been shown in the laboratory to produce superior and unexpected results when compared to prior art gas burners more specifically the gas burners fabricated according to the principles.