On June 20, 2017, about 2000 central daylight time, an Aeronca 7BCM airplane, N2558E, sustained substantial damage during initial climb from the Mahnomen County Airport (3N8), Mahnomen, Minnesota, when it impacted a bean field after a loss of control. The sport pilot was seriously injured. The airplane was owned and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed for the flight, which was not operated on a flight plan. The airplane was departing 3N8 on a local flight. The pilot reported that he had flown the airplane earlier in the day. About 1900, he returned to the airport with the intention of going on a short local flight. He preflighted the airplane, including fuel samples, and taxied to the run-up area where he performed the before take-off checklist items. He departed from runway 35 and the initial takeoff roll was normal. The pilot then noted the airplane was not gaining airspeed and the engine was not developing full power; but he decided to continue the takeoff. Once he was committed to the takeoff, there seemed to be an even "greater loss of power He stated that the airplane did not gain more than 150 ft of altitude. He stated, "The power seemed to still be fading and I was basically 'hanging on the prop' when I decided to initiate a very slight bank (20 degrees)" to avoid a highway and powerlines. He stated that the airplane stalled and impacted a bean field adjacent to the airport. Witnesses reported that the airplane appeared to be going slow and not climbing before the airplane banked to the right and impacted the ground in a nose down attitude. A Federal Aviation Administration inspector examined the airplane. He removed the valve covers and found a rusty valve springs. He stated that he was able to rotate the engine, and the crankshaft and drive train exhibited continuity. The magnetos turned and sparked. Fuel was found in the carburetor bowl. The spark plugs were normal in color and wear. The header fuel tank was ruptured. There was an auxiliary fuel tank in the left wing. The propeller exhibited minimal damage. He checked and confirmed flight control continuity. No preexisting anomalies to the engine and airframe were noted. In the NTSB accident report which the pilot completed, he provided two recommendations on how the accident could have been prevented: 1. "Aborting the takeoff at the first sign of any kind of performance issue…with enough runway to stop plane." 2. Keep the noise canceling headset turned off during takeoffs and landings. He stated, "Perhaps I would have reacted differently (aborted) if my ears told me the same thing as the controls and instruments referring to the increasing loss of power/thrust/lift." At 2015, the surface weather observation at 3N8 was: wind light and variable; visibility 10 miles; sky clear; temperature 20° C; dew point 8° C; altimeter 29.94 inches of mercury. According to the carburetor icing chart, weather conditions at the time of the accident were conducive to moderate icing at cruise power or serious carburetor icing at descent power.