On August 14, 2018, about 1030 mountain daylight time, a Cessna 140 airplane, N89093, was substantially damaged when it was involved in an accident near Marsing, Idaho. The pilot and passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that after entering the airport traffic pattern, he reduced engine power, applied carburetor heat, and conducted a low pass over runway 12 at Sunrise Skypark Airport (ID40), Marsing, Idaho. As the airplane approached midfield, about 60 ft above ground level, the pilot advanced the throttle, but the engine did not respond. The pilot switched fuel tanks from the left to the right. With insufficient runway remaining to land, the pilot then initiated a forced landing to the shallow side of the Snake River, which paralleled the runway. During the forced landing, the airplane impacted water and came to rest upright, partially submerged in the river. The firewall and lower fuselage were substantially damaged. Examination of the wreckage revealed that all engine accessories remained attached to the engine. Due to impact damage to the airframe fuel strainer, an external fuel source was attached to the carburetor inlet fuel line to perform an engine test run. Despite multiple attempts, the engine would not start. The airbox and carburetor were subsequently removed, and the carburetor was partially disassembled. An orange residue consistent with rust was observed in the float bowl, along with residual water. The float bowl and mixture metering sleeve were cleaned using carburetor cleaner, and the carburetor was reassembled. The engine then started, after multiple attempts, at a power setting of 1,800 rpm or more. When engine rpm was reduced below 1,300 rpm, the engine lost power. Once restarted, at 1,700 rpm, a magneto check was performed, and a decrease of 100 rpm for both magnetos was observed. The maximum rpm obtained during the engine run was 2,300 rpm. The carburetor was removed and retained for further examination. The carburetor was examined at the manufacturer’s facility under the supervision of a Federal Aviation Administration inspector. The inspector reported that the throttle shaft was loose in its bushings or mounting to the casting. Movement of the throttle indicated that the accelerator pump was not sealing against the wall of its chamber, which would not provide fuel required to increase power with throttle movement. In addition, when the carburetor was installed on the flow bench, immediate leaks were noted audibly, one at the throttle shaft seals and one in the area of the accelerator pump. Indications of blockage in the idle chambers of the carburetor were present, and at idle ranges, the [fuel] flows were significantly out of specification. Removal of the idle tube revealed significant corrosion and contaminants in that area. Airframe and engine logbooks contained no specific entries related to an overhaul or maintenance on the carburetor.