Kenmore he4 elite gas dryer isn't drying clothes,

My Kenmore he4 elite gas dryer isn't drying clothes, but with the front panel removed, I observed the ignitor glow and the flow of flame which lasted 5 seconds. The dryer would run about 1 1/2 minutes and the heat would come on for another 5 seconds. Is this normal? The dryer isn't drying clothes. If a repair is needed, any suggestions?