On August 18, 1998, at 1208 hours Pacific daylight time, a homebuilt experimental Clark Barnett J4B2 gyroplane, N694, nosed over during a landing at the Yuba County airport, Marysville, California. The aircraft, owned and operated by the pilot under 14 CFR Part 91, was destroyed in the accident sequence. The student pilot sustained minor injuries. Visual meteorological conditions prevailed at the time and no flight plan was filed for the local area personal flight. The pilot stated that he had recently purchased the gyroplane and wanted to test out the new set of rotor blades that had been installed to see if they would spin up. According to the pilot, after he reached a certain speed while on the runway, the gyroplane shot up in the air approximately 50 feet. For a short period of time he was able to level it out, but the plane immediately yawed to the left. The pilot applied right stick and he reported that it seemed like left rudder was being held. After he made a complete circle to the left he decided to land in the dirt by the runway. According to the pilot, he landed nose low and broke the nose wheel off. He reported he slid for 30 feet and nosed over. The pilot stated that the rotor blades, rotor head, and propeller were destroyed. Some damage was done to the tail section and stabilizer. The Federal Aviation Administration investigator reported that the gyrocopter was destroyed after the rotor blades hit the ground. He reported that the pilot had altered the rotor blades.