What was found
(CAN) FUEL SYSTEM CONTAMINATION. LEAVING GROUND ON TAKEOFF, RT ENGINE AGAIN SURGED, COMMITTED TO CONTINUE TAKEOFF - PILOT COMPLETED CIIRCUIT BACK TO BASE. NOTE: SINCE LAST REPAIR; CLEANING FUEL, A/C HAD FLOWN TWICE FOR 3-4 HOURS , NO INCIDENT. AGAIN, FOUND SOME LEFT OVER PARTICLES IN FUEL. AFTER REPAIRS: RUN-UP OK, BUT AMES EXPERIENCED EARS DETECTED SOME PUFFING UNEVEN. MAGNETO TIMING CHECKED: SHOWED (DUAL MAG) 17 - 15 DEGREE BTDC. RETIMER: LT AT 20 DEGREES PER MAN. GIVING RT 18 DEGREES IN LIMITS OF 3 DEGREES. REPLACED LOWER PLUGS. GROUND RUN OK. AIRCRAFT IN-FLIGHT AT THIS TIME. (X)