Kenmore gas oven not lighting, keeps clicking?

I have an older model kenmore gas stove. the oven has a probolem starting. When I turn the knob on, the spark ignition starts and keeps clicking. No gas flows out of the valve, but the pilot lights fine. when I sit and tap the gas valve, it may eventually send gas to the main burners and light. when the main burners kick on, the spark ignitor keeps clicking even though the flame is already lit. The main problem, however, is the pilot is ignited and running, but the gas valve doesn't open to light off the burners. I don't know specifically if it is a stuck valve. Any ideas? The sparking still continues once it does light. Any siggestions are very appreciated