DURING A DEPARTURE CLIMB OUT THE AIRPLANE EXPERIENCED A PARTIAL LOSS OF ENGINE POWER AND MADE A FORCED LANDING WHILE TRYING TO RETURN TO THE AIRPORT. ON SUBSEQUENT EXAMINATION THE CARBURETOR AND PROPELLER WERE DAMAGED AND REPLACEMENTS WERE LOCATED AND INSTALLED. THE ENGINE RAN PROPERLY ON THE RIGHT, LEFT, AND BOTH MAGNETOS. TRACES OF WATER WERE FOUND WHILE DRAINING THE FUEL TANKS.