PA-28 Cherokee/Archer/Dakota/Pillan/Warrior
Flight Crew Commercial; Flight Crew Instrument
Flight Crew Last 90 Days 5; Flight Crew Total 628; Flight Crew Type 150
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Fuel Issue
Air Traffic Control Provided Assistance; Flight Crew Landed As Precaution
Aircraft
The mission was practicing landings at ZZZ on Runway XXR.  Weather was VFR.  All 4 fuel tanks were full at the start of the flight.  No issues were noted with the aircraft during preflight; taxiing; or run-up.  The plane behaved normally for the first two takeoffs and landings.  The engine had been running for approximately 40 minutes at that point; all drawing from the left main tank; with ~60% of the tank remaining. During the climb-out from the 3rd takeoff; at about 700 ft AGL; the engine had a momentary loss of power (lasting about a second).  In an effort to troubleshoot; I switched tanks from left main to right main.  A few seconds later; another momentary loss of power occurred (again lasting about a second).  Note that this was with everything in takeoff configuration; full throttle; max RPM; mixture full rich; electric fuel pump on; and carburetor heat was already on (keeping the carburetor temperature gauge above 40 deg F). At this point I felt there was a significant risk of the engine having an impending permanent loss of power and decided the most expedient option to get the plane safely back on the ground was to do a left 180 deg turn to land in the opposite direction on the parallel runway.  I stated the situation and my intention to the Tower over the radio.  The turn; descent; and landing on XXR were completed uneventfully.  There was no traffic actively using that runway at the time; so that wasn't a factor. At this point; it's unclear what the root cause was for the engine's momentary power losses.  I've contacted my local shop and have no intention of flying the plane again until after they investigate.  Of note; the engine stayed running seemingly normally at idle during the descent; landing; and subsequent taxiing.  However; during taxiing; the engine would run rough at any throttle setting above idle.  Also; during preflight; the tip tanks both had some water that was sumped out; but the main tanks (the only tanks used during the flight) didn't show any noticeable water when sumped.
Pilot reported engine problems and suspected a fuel issue.