Your burner may have a blockage, preventing proper gas and air flow. When cool, remove your burner and inspect the ports. If the ports are blocked, clean with a soft bristle brush. Alternately you can clear the debris out by poking blocked holes with a paper clip (or another tool small enough – never drill or file portholes, enlarging them will damage your burner).
Next, clean out the burner venturi tubes. Use a venturi brush or pipe cleaner and push it through the entire tube while turning. Pull out the brush and examine for any debris. Be aware that spiders are attracted to the smell of gas, and may have taken residence in your venturi tubes. To prevent this, make sure the spider guards are protecting the air intake holes at all times.