What was found
AIRCRAFT WAS GROUNDED: PILOT REPORTS NR 1 ENG VIBRATION FELT AT FL290 WHEN POWER ADVANCED. NO INDICATION UNTIL LEVEL OFF AT 9000 FT. NR 1 ENG N1 VIB FLASHING AT 6.4 AT ABOUT 65% N1, POWER SET AT IDLE FOR REST OF FLIGHT. VIB INDICATIONS NORMAL AT LOW POWER. VERIFIED ENGINE VIBRATIONS DURING ENGINE RUN UP PROCEDURE, WHILE RUNING ENGINES, SMOKE WAS NOTICED COMING FROM THE EXHAUST PLUG AFT SUMP AREA. MAINTENANCE CHECKED THE SCAVENGE SCREENS AND FOUND LARGE QUANTITY OF CARBON LIKE DEBRIS ALONG WITH PIECES OF SAFETY WIRE. MAINTENANCE REMOVED AND REPLACED THE NR 1 ENGINE IAW CARD 26L40071001.