On March 28, 2000, at 1243 eastern standard time, a Alon A-2A, N67HS, collided with trees during takeoff at the 12 Oaks Airport in Hernando, Florida. The airplane was operated by the private pilot under the provisions of Title 14 CFR Part 91 and visual flight rules. Visual meteorological conditions prevailed, and no flight plan was filed for the local flight. The pilot received serious injuries and the airplane sustained substantial damage. The flight was originating at the time of the accident. According to the pilot, just after rotation at approximately 250 feet above ground level (AGL) the engine RPM decayed quickly but smoothly to about 1100 RPM. He steered the airplane straight ahead to clear a large marshy pond area with fields and numerous scatter pine trees, then turned left back towards the airport. He stated that he quickly pulled the throttle out and pushed in forward and the engine RPM returned to about 2100 RPM for about 20 seconds then the RPM decayed to around 1000 RPM. He pulled the throttle out and pushed in forward again, but with no change in RPM. The airplane subsequently impacted trees between two homes. Examination of the engine by Teledyne Continental Motors and the FAA, disclosed that the carburetor accelerator pump did not operate when the throttle was opened. The carburetor was disassembled and the accelerator lower check valve was found contaminated with rusty debris. The acceleration leather plunger was found hard and red in color, similar to the rusty residue. The leather plunger did not fit tightly in the acceleration well. The carburetor bowl exhibited rusty residue in the lower portion. The float level was not measured, but visually appeared normal. Additionally, weather conditions were favorable for the formation of carburetor ice at the time of the accident.