On January 6, 1999, about 1130 eastern standard time, a Piper PA-22-108, N4542Z, registered to a private individual, landed hard then nosed over during a forced landing shortly after takeoff from Middle Georgia Airport, Perry, Georgia. Visual meteorological conditions prevailed at the time and no flight plan was filed for the 14 CFR Part 91 personal flight. The airplane was substantially damaged and the private-rated pilot, the sole occupant, was not injured. The flight was originating at the time of the accident. The pilot stated that before departure, a total of 10 gallons of automotive fuel were added to the fuel tanks; 5 gallons into the left and right fuel tanks. He then performed a preflight with no discrepancies noted. After takeoff while climbing through 200 feet, the engine rpm decreased to 1,500 rpm. He pumped the throttle, which had no effect. While descending for a forced landing on a nearby sod farm, the airplane stalled, landed hard in a field short of the intended touchdown location (sod farm) and nosed over. Examination of the airplane at the accident site by an FAA airworthiness inspector while the airplane was inverted revealed fuel leakage from the right wing fuel tank cap. The airplane owner/pilot reported that during recovery of the airplane, he noted that the carburetor bowl was damaged and the carburetor control was connected at the carburetor. Further examination of the engine following recovery revealed that the differential compression readings (cold) from cylinder Nos. 1, 2, 3, and 4 were 20, 19, 54, and 5 psi respectively. The valve adjustment for the No. 2 cylinder was then loosened and the cold differential compression reading increased to 50 plus psi. The fuel selector was determined to be improperly assembled; no detent for each position could be felt. Marks were noted adjacent to the fuel selector which coincided with fuel selector position. Fire damage was noted to the inside portion of the bracket type air filter element, and the sending unit for the right wing fuel tank was improperly installed. With respect to the carburetor, a two-piece venturi was installed, which according to the FAA inspector, was required by Airworthiness Directive to be changed to a one-piece venturi. Review of the maintenance records revealed an entry dated April 21, 1997, which indicates that all valve rocker arms were adjusted and a one-piece venturi was installed. The airplane had accumulated approximately 85 hours since the valve adjustment at the time of the accident.