On April 08, 1994, at 1755 Alaska daylight time, a wheel equipped Helio Courier airplane, N42DC, registered to Wright Air Service, Inc. of Fairbanks, Alaska, experienced a total loss of engine power while in cruise flight approximately 40 miles southeast of Manley Hot Springs, Alaska. The airline transport certificated pilot-in-command and his one revenue passenger were not injured and the airplane sustained substantial damage during the ensuing off airport emergency forced landing on a small frozen lake. The 14 CFR Part 135 on demand flight last departed Fairbanks at about 0855 and the destination was the passengers home near the Cosna River. The pilot reported that at the time of the accident, visual meteorological conditions prevailed in the area of the mishap site and that a VFR flight plan was on file with the Flight Service Station (FSS) in Fairbanks. The pilot reported that about 25 minutes into the flight light snow showers were encountered and that about one hour into the flight the snow showers became more intense reducing the inflight visibility to about 3 miles. Then while in cruise flight at an altitude of 3500 feet msl and about 10 miles from the destination the engine suddenly stopped with no warning. Carburetor heat was applied, the fuel boost pump was turned on and the magneto's and fuel valve were check but to no avail. Company A&P mechanics were flown to the mishap site the following day. Their finding was that the fuel vent located on the top left wing had been bent back allowing snow to become impacted through the curve of the line. This situation would produce a significant reduction in fuel flow to the engine. Company personnel offered the comment that the vent may have become bent during the removal of snow from the upper surface of the wing by brooming.