Your burners should have small air holes (not to be confused with the circling burner ports) that face the center of the oven. These holes help bring in the air necessary for combustion inside your burner system. If they become clogged, the burner will not work, will light slowly or will have a weak flame. You can fix this problem by finding the air holes and cleaning them with a toothpick or other small object.
The burner ports themselves, which let gas into the burner, can also become clogged. This is usually due to a buildup of grease and soot that occurs over time. The fix is similar to clearing the air holes. Use a small piece of wire or a needle to clear the burner ports and restore function to the burner. After clearing the ports, the burner should light evenly and easily.
When cleaning burner ports, make sure the burner is completely off and that there is no chance of it accidentally turning on. Do not use a toothpick when cleaning the burner ports to avoid wood shavings that can ignite and cause further clogs. Do not try to bend or enlarge any of the ports, which are designed to channel a specific flow of gas.
If your burners still seem to be acting weak after you have cleaned them, the problem could lie farther down the gas line. The line may have a blockage or failed valve. To fix the problem, call in a professional to examine your gas lines and test or replace valves.