WHILE ATTEMPTING TO TAKEOFF FROM A PVT GRASS STRIP OF ABOUT 2000 FEET IN LENGTH, THE ACFT WAS UNABLE TO ESTABLISH A POSITIVE CLIMB, AND SETTLED BACK TO THE TERRAIN. THE FINAL DESTINATION WAS TO BE FAIRBANKS, ALASKA, FOR A HUNTING TRIP. THE ACFT WAS LOADED WITH BAGGAGE, HUNTING GEAR, FIREARMS, PILOT AND TWO ADULT PASSENGERS. THE ACFT HAD BEEN CONVERTED TO A TAIL WHEEL CONFIGURATION AND IN ADDITION WAS EQUIPPED WITH LARGE, OVERSIZE, 'TUNDRA TYPE' TIRES. POST ACCIDENT INVESTIGATION REVEALED NO MECHANICAL OR FUEL SUPPLY MALFUNCTIONS.