As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAKEOFF ROLL, PILOT REPORTED A STRONG ELECTRICAL BURNING TYPE ODOR IN THE COCKPIT. TAKEOFF ABORTED. ACFT RETURNED TO GATE UNEVENTFULLY. NO CREW OXYGEN WAS UTILIZED. MAINTENANCE FOUND A SMALL PIECE OF RUBBER IN THE NR 2 ACM DUCTING. REMOVED AND AIRCRAFT AND AIRCRAFT RTS.