Narrative:

Did the preflight as usual and nothing stood out of the ordinary. It had 7.5 qt of oil and 1/2 tank of fuel in each tank. Slight tire wear on the left main wheel with no chord showing.engine start was smooth with two primes. Both oil pressure and temp remained in green and the battery was charging fine. During taxiing to the run up engine was running fine at 1000 RPM. All engine gauges were in green.engine run up started with auxiliary fuel pump on for a second just to see the rise in fuel flow. Throttle was advanced to 1800 RPM for the mag check.before starting the mag check the engine seemed to be rough running. So throttle was advanced to 2100 RPM and the leaned the mixture and kept it running for 30 seconds. Then brought back the throttle to 1800 RPM for the mag check with the mixture turned rich about 2 turns in but completely rich. The left and right mag drop were within limitations. All engine gauges were green. Throttle idle check was within limits.after; we went for pattern work and completed 3 patterns to a full stop taxi back with no engine problem.on the 4th pattern; a soft field take off configuration was chosen; with flaps set 10 degrees. As we were cleared for takeoff; mixture was put to full rich; and throttle advanced to full. After main wheels came off of runway; airplane was flown in ground effect until climb speed; at which point the engine was noticed to be 'pulsing'; lightly at first but getting rapidly worse; a cross check of engine gauges indicated all were in the green; and vsi was indicating a no-climb situation at 250 feet AGL. The power was noticeably decreased to the point; with the throttle still at full power setting. As a result; the attitude was pitch up in an attempt to climb but this did no good. The flight controls were transferred to the CFI at this point; and a right turn to attempt a landing on the opposite; adjacent runway was initiated. Instructor informed tower that engine was running rough and needed to immediately return for landing on the opposite runway. Tower cleared to land on 30R. The turn was steepened due to power lines observed near to the aircraft and the stall horn sounded; indicating the low airspeed; seen around 55 KTS by both the student and the instructor. After aligning on 30L; [another] aircraft was seen by the CFI aborting its takeoff roll and the CFI sidestepped to runway 30R. The aircraft touched down midfield on its right main landing gear; followed by left and then nose gears; still with 10-degrees of flaps from the soft field configuration takeoff. The aircraft on a short final was instructed by tower to go around. Took taxiway C under own power; with roughness observed while taxiing. ATC asked if assistance was required; which was declined. While taxiing at 1500 RPM; not enough momentum was being provided as at 1000 RPM; but was still sufficient to return to [the] ramp.after returning to the main ramp; a brief run-up was preformed; with slight roughness noted at around 2100 RPM. Aircraft was then shut down according to checklist.

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Original NASA ASRS Text

Title: C172 Flight Instructor reported that during climb the with engine throttle set at full power the aircraft was unable to climb and the engine power was decreasing.

Narrative: Did the preflight as usual and nothing stood out of the ordinary. It had 7.5 QT of oil and 1/2 tank of fuel in each tank. Slight tire wear on the left main wheel with no chord showing.Engine start was smooth with two primes. Both oil pressure and temp remained in green and the battery was charging fine. During taxiing to the run up engine was running fine at 1000 RPM. All engine gauges were in green.Engine run up started with auxiliary fuel pump on for a second just to see the rise in fuel flow. Throttle was advanced to 1800 RPM for the mag check.Before starting the mag check the engine seemed to be rough running. So throttle was advanced to 2100 RPM and the leaned the mixture and kept it running for 30 seconds. Then brought back the throttle to 1800 RPM for the mag check with the mixture turned rich about 2 turns in but completely rich. The left and right mag drop were within limitations. All engine gauges were green. Throttle idle check was within limits.After; we went for pattern work and completed 3 patterns to a full stop taxi back with no engine problem.On the 4th pattern; a soft field take off configuration was chosen; with flaps set 10 degrees. As we were cleared for takeoff; mixture was put to full rich; and throttle advanced to full. After main wheels came off of runway; airplane was flown in ground effect until climb speed; at which point the engine was noticed to be 'pulsing'; lightly at first but getting rapidly worse; a cross check of engine gauges indicated all were in the green; and VSI was indicating a no-climb situation at 250 feet AGL. The power was noticeably decreased to the point; with the throttle still at full power setting. As a result; the attitude was pitch up in an attempt to climb but this did no good. The flight controls were transferred to the CFI at this point; and a right turn to attempt a landing on the opposite; adjacent runway was initiated. Instructor informed tower that engine was running rough and needed to immediately return for landing on the opposite runway. Tower cleared to land on 30R. The turn was steepened due to power lines observed near to the aircraft and the stall horn sounded; indicating the low airspeed; seen around 55 KTS by both the student and the instructor. After aligning on 30L; [another] aircraft was seen by the CFI aborting its takeoff roll and the CFI sidestepped to Runway 30R. The aircraft touched down midfield on its right main landing gear; followed by left and then nose gears; still with 10-degrees of flaps from the soft field configuration takeoff. The aircraft on a short final was instructed by tower to go around. Took taxiway C under own power; with roughness observed while taxiing. ATC asked if assistance was required; which was declined. While taxiing at 1500 RPM; not enough momentum was being provided as at 1000 RPM; but was still sufficient to return to [the] ramp.After returning to the main ramp; a brief run-up was preformed; with slight roughness noted at around 2100 RPM. Aircraft was then shut down according to checklist.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.