On October 14, 2021, about 1722 eastern daylight time, an experimental amateur built Kitfox IV airplane, N9259M, was substantially damaged when it was involved in an accident near North Canaan Airport (CT24), North Canaan, Connecticut. The private pilot sustained serious injuries. The airplane was operated by the pilot as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that the purpose of flight was to see the fall foliage and it was the first flight of the day. After topping off the fuel tanks, he started the engine, warmed it up to “takeoff temps[sic],” checked the magnetos, and departed to the north. During the climbout, the airplane had cleared trees at the departure end of the runway; however, the “engine sputtered.” He subsequently checked the “[magneto] switches, fuel switches, fuel pressure” and all were “good.” He then turned 180° to the airport, however, the airplane was “too high too fast” to land toward the south so he “tried [the] throttle again,” the power came up, and he continued south. Subsequently, the trees at the southbound departure area were cleared; however, shortly thereafter, the “engine sputtered again” as the throttle was increased toward full power. The pilot reported that at this time the airplane was “too close to trees”, the airplane descended, and then he “pulled up and bellied into the trees, to an almost stop,” however, the airplane then fell nose first about 70 ft into mud and swampy terrain. The pilot further reported that he utilized full carburetor choke via the spring-loaded lever to start the engine, then utilized half choke as the engine warmed up. He could not remember shutting the choke off before takeoff and also did not recall checking the choke position in-flight while troubleshooting the partial loss of engine power. He described that the engine would sputter at full power but would run without issue at idle power. Photographs revealed that the airplane came to rest in wooded terrain partially submerged in a creek and mud, with the fuselage nearly vertical and the engine submerged below the terrain and water. The fuselage and both wings sustained substantial damage. There was a smell of fuel at the accident site. Examination of the airplane did not reveal any evidence of preimpact mechanical malfunctions or failures that would have precluded normal operation. Continuity of the flight controls and fuel system was confirmed. Photographs taken shortly after the accident found that the carburetor choke lever was in the stowed position. The airplane was not equipped with carburetor heat. According to a representative of Kitfox Aircraft, the type of choke installed of the accident airplane would remain on/ open until the pilot turned the choke off. According to a carburetor icing probability chart, the weather conditions at the time of the accident flight were conducive to serious icing at glide power.