I was recently plagued by a slow/weak burner on my otherwise fine Gas stove.  This unit has sealed gas burners that are near impossible to remove.  The most common cause of a weak gas burner is a plugged orifice where the gas enters the burner.  This can be caused by a severe boil-over, cleaners or other gunk getting into the burners.  The end result is the burner won’t start or has a very weak flame.