I had a similar issue with one of my burners. After troubleshooting the system I found the problem. It was a blocked orifice fitting (brass fitting in the burner). When I disconnected the line from the fitting, I found small pieces of Teflon tape blocking the orifice. Apparently some small pieces came off after I re-assembled the gas manifold. Yes I know, you should clean the threads before re-assembling the system (learned my lesson!).
Hope this helps.