According to the pilot, about 20 minutes into a local flight, he observed smoke entering the cockpit of the experimental amateur-built helicopter while he was executing a turn. The pilot initiated a precautionary autorotation to a hayfield. After landing, he observed flames emanating from the lower aft left side of the fuselage, which quickly intensified. The pilot exited the helicopter and contacted emergency services. A Federal Aviation Administration inspector who responded to the accident site reported that the helicopter had been largely consumed by the fire. Examination of the wreckage revealed that the entire fuel system had been destroyed. A review of maintenance records indicated that both fuel lines to the fuel pumps had been replaced 13 flight hours before the accident due to a low fuel pressure anomaly. Due to the extent of the fire damage, the origin of the fire could not be determined.