The pilot of the tailwheel-equipped airplane reported that, the mixture control had been "working really hard" during the initial flight, so he landed at a remote site to investigate. Once on the ground, he found that the mixture control cable, just behind the instrument panel, had failed. He manually opened the mixture control lever and departed for his destination airport. While en route, at about 700 ft above ground level the engine lost all power. He made an emergency off-airport landing to a heavily forested area and the airplane impacted several small to medium sized spruce trees. The airplane sustained substantial damage to the wings and left lift strut. The pilot stated that after the accident, he found the mixture control arm had that the mixture control arm had become detached from his previous temporary repair, and it was in the closed position. Additionally, he noted that he made a poor decision to fly the airplane with a failed mixture control cable.