The pilot intended to conduct an aerial inspection of one of his properties prior to departing for his home base. The pilot reported that during the takeoff the engine misfired, so he abandoned the takeoff and returned to the threshold of the airstrip where he carried out a complete engine run which satisfied him that all was normal. The subsequent take-off was uneventful, and the pilot completed the property inspection. Several minutes after setting heading the engine again misfired, accompanied by backfiring and a loss of power. The pilot attempted to return to the airstrip on his property, but the lack of power committed him to a forced landing. He selected a suitable flat open cultivated paddock and made a successful landing. Vacating the aircraft the pilot noticed a fire burning in the engine bay area, which increased in intensity and completely consumed the aircraft. This accident was not the subject of an on-scene investigation.