The experimental homebuilt aircraft was being demonstrated by the pilot to a potential buyer, who was a passenger in the rear tandem seat. The engine did not have an electric starter installed on the engine. According to the passenger, the pilot was demonstrating the low speed handling characteristics of the aircraft at an altitude he estimated at about 3,000 feet AGL. The pilot brought the throttle to idle, and, as the aircraft slowed, the engine ceased to run and the propeller stopped turning. The pilot was unable to affect an airstart of the engine and the aircraft collided with the ground while the pilot was attempting a forced landing on a road. Detailed examination of the engine revealed no evidence of a preimpact mechanical malfunction or failure. The emergency procedures section of the aircraft owners manual states that an airspeed of 70 knots or more is required to maintain engine rotation at idle. The manual further states that if the engine stops turning, a dive speed of 130 knots or more is required to regain engine rotation with an altitude loss of greater than 2,000 feet.