What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
(-23) On initial pushback the crew attempted to start the #1 engine. It failed to start. A determination was made that the left ignition system was inoperative. The crew determined to continue to taxi and use the right ignition system on taxi-out to start the #1 engine. They then started the #2 engine and proceeded to taxi toward the departure runway. While taxiing they motored the #1 engine in an attempt to rid it of any pooled fuel. Prior to reaching the active runway the crew again attempted to start the #1 engine using the right ignition system. There was apparently some residual pooled fuel in the tail pipe that ignited causing the tail pipe fire. After returing to the gate the engine was inspected. The left ignition system was deferred per delta's procedures and the aircraft departed for great falls.
As the FAA filed it
(-23) ON INITIAL PUSHBACK THE CREW ATTEMPTED TO START THE #1 ENGINE. IT FAILED TO START. A DETERMINATION WAS MADE THAT THE LEFT IGNITION SYSTEM WAS INOPERATIVE. THE CREW DETERMINED TO CONTINUE TO TAXI AND USE THE RIGHT IGNITION SYSTEM ON TAXI-OUT TO START THE #1 ENGINE. THEY THEN STARTED THE #2 ENGINE AND PROCEEDED TO TAXI TOWARD THE DEPARTURE RUNWAY. WHILE TAXIING THEY MOTORED THE #1 ENGINE IN AN ATTEMPT TO RID IT OF ANY POOLED FUEL. PRIOR TO REACHING THE ACTIVE RUNWAY THE CREW AGAIN ATTEMPTED TO START THE #1 ENGINE USING THE RIGHT IGNITION SYSTEM. THERE WAS APPARENTLY SOME RESIDUAL POOLED FUEL IN THE TAIL PIPE THAT IGNITED CAUSING THE TAIL PIPE FIRE. AFTER RETURING TO THE GATE THE ENGINE WAS INSPECTED. THE LEFT IGNITION SYSTEM WAS DEFERRED PER DELTA'S PROCEDURES AND THE AIRCRAFT DEPARTED FOR GREAT FALLS.