As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER THE SECOND LANDING, THE THROTTLE WAS PULLED BACK BUT THE ENGINE RPM WOULD NOT GO BELOW 1900 RPM. UPON OPS AND VISUAL INSPECTION IT WAS DETERMINED THAT THE CARBURETOR ACCELERATOR PUMP DISCHARGE TUBE HAD COME LOOSE FROM ITS MOUNT AND LODGED IN THE THROTTLE VALVE PLATE, CAUSING THE "STUCK" AT 1900 RPM INDICATION. UPON EXCERSISING THE THROTTLE THE PUMP DISCHARGE TUBE FELL DOWN TO THE CARBURETOR HEAT BOX BELOW THE CARBURETOR AND INTERFEERED WITH THE OPERATION OF THE CARBURETOR HEAT VALVE. THE CARBURETOR WAS REPLACED.