On May 21, 1995, about 0950 eastern daylight time, a Grumman G-164A, N35RA, registered to Robert S. Kafka, nosed over while making a forced landing following loss of engine power at Zellwood, Florida, while on a 14 CFR Part 91 aerial advertising flight. Visual meteorological conditions prevailed at the time and no flight plan was filed. The aircraft sustained substantial damage and the airline transport-rated pilot was not injured. The flight was originating at the time of the accident. The pilot stated that he performed a preflight inspection of the aircraft and found the fuel tank to be full. He drained the fuel system sump drains. After takeoff from Crakes Farm Strip he returned to the strip and picked up an aerial advertising banner. During climbout from the banner pickup the aircraft reached about 300 feet at which time he noticed it was not climbing. He increased engine power; however, the aircraft would not maintain airspeed or climb. He lowered the aircraft's nose and dropped the banner. While making a forced landing in a soft field planted with celery, the aircraft nosed over. Postcrash examination of the engine, engine accessories, and propeller was performed by FAA inspectors. No evidence to indicate precrash failure or malfunction of the engine or propeller was noted.