What was found
(CAN) DURING START OF NR 1 ENGINE, THERE WAS A SIGNIFICANT FUEL LEAK. ACFT RETURNED TO GATE AND PASSENGERS DEPLANED. MAINTENANCE CARRIED OUT TO TWO IDLE RUNS AS PART OF THE VENTS AND DRAINS INSPECTION IAW AMM 71-71-00-200-801-F00 AND NO FURTHER LEAKS WERE NOTED. ACFT RETURNED TO SERVICE. THE VENTS AND DRAINS INSPECTION WAS CARRIED OUT AND THE OFFENDING COMPONENT IDENTIFIED AND REPLACED.