Narrative:

I was departing from ZZZ when I experienced a partial loss of power during take-off. The pre-take off run up and magneto checks were normal with appropriate RPM drop with the engine at 2000 RPM. Appropriate RPM drop was noted when carburetor heat was applied. Fuel selector switch was set to the fullest tank (right tank). Flaps were set to the 1st notch.take-off roll was normal and the aircraft lifted off in the expected length of runway use. Once positive rate of climb was established while still over the runway; the flaps were retracted. Immediately upon the raising of the flaps; the engine began to run rough and was not producing full power. After the aircraft settled a bit; I was able to maintain level flight and hold altitude; but it did not appear that I was able to climb.I applied carburetor heat with no effect. I switched the fuel selector switch to the left tank with no immediate effect. I left the fuel selector switch on the left tank. I estimate that the fuel quantity in the left tank was between 5-10 gallons and the fuel quantity in the right tank was between 10-15 gallons at the time of take-off.I decided to continue flight straight ahead rather than risk a low altitude turn to return to the runway. I knew that the terrain would fall off as I neared the harbor and the water. I felt that if a forced landing would be required; it would be preferable to do so in the water rather than in the trees. My intention was to continue flight as long as I could hold altitude and try to fly a normal pattern to return to land on runway xx.I was able to clear the trees at the end of runway xx and turn crosswind over the water at the harbor. Shortly after reaching the harbor area the roughness of the engine resolved itself and I was able to extend the downwind and climb to 3500 ft. I suspected that the partial power loss may have been due to moisture or debris in the fuel. Note; the pre-flight fuel sample taken earlier that morning was free of water or debris. The engine continued to provide full power; so I returned the fuel selector switch to the right tank and decided to continue the return flight to ZZZ1 where the aircraft is based. The remainder of the flight was uneventful and the roughness to the engine and associated partial power loss did not return.upon landing; I sampled the fuel from each tank as well as the gascolator and observed no water or debris. The electrical connections to the magnetos and spark plugs appear normal with no loose or frayed wiring.I am submitting this report because a fly-in was being held at the ZZZ on that particular day and many fellow pilots as well as the general public observed the partial loss of power and the low altitude departure and proximity of my aircraft to the trees at the departure end of runway xx. ZZZ [area] residents or members of the general public may improperly assume that the low altitude was and intentional act -- rather than due to the partial power loss to the engine on departure.

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Original NASA ASRS Text

Title: GA pilot reported engine roughness after takeoff.

Narrative: I was departing from ZZZ when I experienced a partial loss of power during take-off. The pre-take off run up and magneto checks were normal with appropriate RPM drop with the engine at 2000 RPM. Appropriate RPM drop was noted when Carburetor Heat was applied. Fuel selector switch was set to the fullest tank (Right Tank). Flaps were set to the 1st notch.Take-off roll was normal and the aircraft lifted off in the expected length of runway use. Once positive rate of climb was established while still over the runway; the flaps were retracted. Immediately upon the raising of the flaps; the engine began to run rough and was not producing full power. After the aircraft settled a bit; I was able to maintain level flight and hold altitude; but it did not appear that I was able to climb.I applied Carburetor Heat with no effect. I switched the fuel selector switch to the left tank with no immediate effect. I left the fuel selector switch on the left tank. I estimate that the fuel quantity in the left tank was between 5-10 gallons and the fuel quantity in the right tank was between 10-15 gallons at the time of take-off.I decided to continue flight straight ahead rather than risk a low altitude turn to return to the runway. I knew that the terrain would fall off as I neared the harbor and the water. I felt that if a forced landing would be required; it would be preferable to do so in the water rather than in the trees. My intention was to continue flight as long as I could hold altitude and try to fly a normal pattern to return to land on Runway XX.I was able to clear the trees at the end of runway XX and turn crosswind over the water at the harbor. Shortly after reaching the harbor area the roughness of the engine resolved itself and I was able to extend the downwind and climb to 3500 ft. I suspected that the partial power loss may have been due to moisture or debris in the fuel. Note; the pre-flight fuel sample taken earlier that morning was free of water or debris. The engine continued to provide full power; so I returned the fuel selector switch to the right tank and decided to continue the return flight to ZZZ1 where the aircraft is based. The remainder of the flight was uneventful and the roughness to the engine and associated partial power loss did not return.Upon landing; I sampled the fuel from each tank as well as the gascolator and observed no water or debris. The electrical connections to the magnetos and spark plugs appear normal with no loose or frayed wiring.I am submitting this report because a fly-in was being held at the ZZZ on that particular day and many fellow pilots as well as the general public observed the partial loss of power and the low altitude departure and proximity of my aircraft to the trees at the departure end of runway XX. ZZZ [area] residents or members of the general public may improperly assume that the low altitude was and intentional act -- rather than due to the partial power loss to the engine on departure.

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.