On August 26, 2000, at 1409 hours Pacific daylight time, an experimental Steinke Early Bird-Jenny, N593JN, sustained substantial damage during a forced landing near Chino, California. The forced landing was precipitated by a loss of engine power during the approach to the Chino airport. The private pilot/owner was operating the airplane under the provisions of 14 CFR Part 91, and was not injured. The personal flight departed Rubideaux Airport, Riverside, California, about 1400. Visual meteorological conditions prevailed and no flight plan had been filed. The pilot told the Federal Aviation Administration (FAA) accident coordinator that the airplane ran well when he flew from Chino to Riverside. On the return to Chino, the engine lost power during cruise flight at 1,800 feet mean sea level (msl). He told the inspector he turned on an auxiliary electric fuel pump and utilized the primer, but the engine did not regain power. The airplane landed in a field about 1/2 mile from the runway and nosed over to an inverted position. The FAA coordinator inspected the airplane. Movement of the throttle valves inside the carburetors corresponded to movement of the throttle lever inside the cockpit. Each fuel tank was at half capacity. A mechanic operated the primer button and he observed fuel being injected into the carburetor intake body. He noted the vacuum fuel pump was the primary feed for the engine. This pump could not be tested, as the engine could not be run. He tested the electric fuel pump. This pump operated after he vigorously cycled the master power switch several times between the on and off positions. He observed that the spark plugs were not wet with fuel or oil. They exhibited characteristics of normal operation when compared to the Champion Aviation Check-A-Plug AV-27 Chart.