On July 29, 1998, at 1730 central daylight time, an Aero Commander 685, N414C, received substantial damage on impact with terrain during a forced landing to runway 30 (2,971 ft x 38 ft, asphalt/dry) at Morey Field near Middleton, Wisconsin. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 91 personal flight was operating on a instrument flight plan. The pilot and one passenger reported no injuries. The flight originated at Ryan Field Airport, near Tucson, Arizona, at 1212 and was en route to Whittman Regional Airport near Oshkosh, Wisconsin. The pilot reported that he had instructed the line personnel at Ryan Field to "top the aircraft off" and upon completion, the line personnel informed the pilot that the aircraft had been "topped off". The pilot stated that he did not visually verify the fuel level within the tanks nor did he "dip stick" the tanks. The pilot did not notice a fuel stain on the top of either wing prior to takeoff. Five hours after departure at flight level 250, a descent was initiated, and at flight level 200, the left engine began to run rough and the fuel pressure began fluctuating. The pilot shut the engine down after having selected the high boost pump, which did not stabilize the engine, and having attempted to restart the engine with no success. Approximately 2-3 minutes had elapsed when the right engine began to display the same symptoms. The pilot feathered both propellers, declared an emergency and attempted a landing at Morey Field but landed 1000 ft short of the runway in soft dirt. The pilot stated that at 1500 ft above ground level (agl), he had the field made and intended to land on runway 30. He felt that at 500 ft agl, that the aircraft was still high and figured that the gear would take a "little while" to come down. The pilot deployed the landing gear through the use of the emergency gear extension system. The pilot also stated that the gear deployed sooner than expected and realized that he was not going to make the runway. The aircraft landed approximately 1000 ft short of runway 30. The piloted stated that there should have been 80 gallons of fuel remaining; the gauge indicated 80-85 gallons of fuel. The aircraft was then ferried to a repair station for repairs. The pilot reported that he owned the aircraft for approximately two months and had received a checkout in this aircraft which lasted about 2.0 hours in duration. Upon the aircraft's arrival, the repair station reported that, "there was considerable fuel stain present from the left outboard fuel filler cap". The fuel cap was removed and its underlying flapper was pushed downward. In doing so, a tremendous amount of vacuum was reported to be present. The left and right fuel vent lines were both blocked with mud debris which was attributed, by the repair station, to be from a common wasp that favors fuel vents on many types of aircraft. The aircraft was weighed with and without fuel on board and was reported to hold 319 gallons of fuel, after a the temperature of fuel stabilized at 72 degrees F. A Federal Aviation Administration Inspector had drained a total of a 1/2 gallon of fuel from the fuel tanks. The fuel gauge indicated 55 gallons of fuel when the electrical master switch was turned "ON". There were fuel stains present on top of the wings during the field inspection of the aircraft. The Aero Commander 685 Flight Manual lists the usable fuel capacity with optional fuel tanks to be 322 gallons. A review of fuel records indicate that the airplane was fueled twice prior to departure. Fuelling records provided by the fixed base operator who had fuelled the aircraft show that the aircraft was refueled twice on July 15, 1998 to obtain 278.0 gallons and 13.5 gallons of fuel. The Aero Commander 685 Maintenance Manual provides a "Indicator Error Envelope" for the fuel system which depicts the maximum allowable tolerance between the weight of fuel in the tanks and the fuel quantity gauge indication. At 0 lbs of fuel in the tanks, the fuel gauge has an error tolerance of +/-35 lbs and at 3250 lbs of fuel the error tolerance is +175 lbs and a -170 lbs. The manual also states, "The fuel vent outlet tube on the lower wing surface should be checked daily for evidence of foreign material". The Aero Commander 685 Flight Manual also states that the left and right fuel vent should be checked during the preflight inspection.