What was found
DURING LEFT ENGINE START ONLY, DUCT PRESSURE GAUGE FLUCTUATIONS 10-30PSI AND ONLY ABLE TO ACHIEVE 16% N2 VERY SLOW TO SPOOL, NO PARAMETERS EXCEEDED. RT START NORMAL. AIRCRAFT BACK TO BLOCK AND GROUNDED BY MAINTENANCE. REMOVED AND REPLACED K10247 AND K10250, L & R ENG START 2 RELAYS. REMOVED AND REPLACED APU SURGE VALVE IAW B767 AMM 49-53-01. OPS CHECK GOOD. DUCT PRESSURE STAYED AT 38PSI THROUGHOUT START AND L ENG N2 2890 AT MAX MOTOR. OPS CHECK GOOD. A/C REMAINS ETOPS 180. AIRCRAFT RETURNED TO SERVICE.