The pilot reported that the takeoff and initial climb were normal. He stated that about 300 feet above ground level (agl), the engine lost power. He lowered the airplane’s nose to establish a glide and set-up for a forced landing. He executed an emergency landing to an area of tall grass adjacent to a pond. The pilot noted that the airplane “stalled out perhaps 5 [feet] or 10 [feet] above the 5 [foot] high grass – then came down hard.” The airplane sustained substantial damage to the rear wing spar and attachment fittings. A post accident inspection revealed that the carburetor fuel inlet screen was blocked with metal particles, sand, dirt, insects and other debris. The pilot stated that although he had inspected the gascolator screen, he had not inspected the fuel system screens. The pilot was also the owner and builder of the amateur-built airplane.