A combustion system includes a perforated flame holder, an oxidant source, and an adjustable fuel nozzle. The oxidant source outputs oxidant. The adjustable fuel nozzle outputs fuel onto the perforated flame holder. The perforated flame holder supports a combustion reaction of the fuel and oxidant within the perforated flame holder. The position of the adjustable nozzle relative to the perforated flame holder can be adjusted to achieve selected characteristics of the combustion reaction within the perforated flame holder.