On April 5, 1998, about 1500 Eastern Standard Time, a Piper PA-18-150 Super Cub, N4158Z, was substantially damaged during a forced landing to a field near Berkley, Massachusetts. Neither the certificated private pilot nor the passenger were injured. Visual meteorological conditions prevailed. No flight plan had been filed for the local flight conducted under 14 CFR 91. According to a Federal Aviation Administration Inspector, the pilot stated that the airplane's engine began to lose power and sputtered while in cruise flight. The application of carburetor heat had no effect, so the pilot landed in a grass field, into the wind. During rollout, at a speed of 10 to 15 miles per hour, the airplane entered a furrow between two fields and nosed over. The Inspector also noted that the airplane "was equipped with tundra tires and disc brakes positioned on the front of the brake assemblies as opposed to the rear as most commonly observed." Damage occurred to the fuselage, vertical fin, propeller and both wings. Fuel was sampled from both tanks and the gascolater, and found to be clear. The carburetor was secure, and the venturi and bleed tube were in place. A carburetor Airworthiness Directive had been accomplished during the last annual inspection. A post-accident engine test run was completed, with normal indications. The passenger, also a pilot, stated he was not flying the airplane at the time of the accident, but had flown it from Kentucky to Massachusetts several days earlier. During that flight he had experienced the same engine problem, but resolved it with the application of carburetor heat. The pilot, seated in the front seat, held a Private Pilot certificate and had approximately 350 hours of flight time. The passenger, seated in the back seat, held Airline Transport Pilot and Flight Instructor certificates, and had approximately 7,000 hours of flight time.