A mechanic reported that the maximum engine rpm attained during a postmaintenance full-power engine run earlier on the day of the accident was between 2,300 and 2,375 rpm; he approved the airplane to return to service. (A maximum continuous power setting of 2,650 to 2,700 rpm was required.) The airplane had not flown in about 14 months. A postmaintenance check flight was not performed after the annual inspection.A flight instructor and a pilot under instruction were initiating a personal flight, which was the airplane’s first flight after the annual inspection was completed.  Coincidentally, it was also their first flight in the same airplane in which they experienced poor takeoff and climb performance during a flight nearly 14 months earlier.Witnesses reported that during the accident takeoff roll, the engine did not sound normal, with one reporting that it never sounded smooth the entire time the airplane was on the runway or while airborne. The airplane became airborne about 3,311 ft down the 6,201-ft runway, which was about 2,087 ft more takeoff distance than the calculated value for the environmental conditions that day. After becoming airborne, the airplane leveled off at 25 ft followed by a momentary power reduction and then a power advance. The flight continued in a shallow climb, climbing no higher than about 50 to 200 ft when the flight was about 5,200 ft down the runway with about 1,000 ft of runway remaining. The flight continued off the airport where the “poor” engine sound continued. While maintaining controlled flight, the airplane impacted a storage structure attached to an apartment building, resulting in a postimpact fire that nearly consumed the airplane.Postaccident examination of the engine revealed that none of the two-piece fuel injector nozzles had inserts or restrictors installed The mechanic reported that the fuel injector nozzles Page 2 of 12 ERA23FA033were cleaned as part of the annual inspection. It is likely that at some point after removing the inserts or restrictors for cleaning, they were not reinstalled. Operational testing of the fuel injector nozzles without inserts or restrictors revealed extensive leakage. Operational testing of a four-cylinder engine of the same manufacturer revealed that without inserts or restrictors installed in any cylinder, the engine produced about 7% less horsepower at full power when compared to a baseline run of the same engine with all inserts or restrictors installed. There were no other engine or engine systems discrepancies noted.Acoustic analysis of the engine indicated that, as the airplane became airborne and immediately before impact, the engine was operating about 2,400 rpm, which was about 11% less than the maximum continuous power setting of 2,700 rpm. Although the engine rpm at the start of the takeoff could not be determined from the available evidence, based on the postaccident engine testing and the extended ground roll distance, it was likely at a significantly decreased value, consistent with the 2,400 rpm recorded during two separate points later during the flight. The mechanic likely incorrectly identified the maximum rpm value obtained during the post-maintenance engine run as falling within the normal operating range, and he did not recognize that with a constant-speed propeller installed the maximum full-power static rpm was specified to be within 50 rpm of the full-power value of 2,700 rpm. As such, the airplane should not have been returned to service. The flight instructor and the pilot under instruction likely did not recognize during the takeoff roll that the engine was producing about 2,400 rpm instead of the normal 2,700 rpm. They also should have recognized that the ground run was excessive and aborted the takeoff while still on the runway. A witness reported that shortly after takeoff, when the airplane was about 25 ft above the runway, he heard a power reduction followed by a power advance. It is possible that the pilots initiated a rejected takeoff but chose to continue the flight, likely due to the limited remaining runway available for landing.