As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF BLACK SMOKE CAME FROM UNDER FLOORBOARDS OF ROWS 2 AND 3, ACRID AS IF ELECTRICAL. TURNED THE BLEEDS OFF AND THE SMOKE STOPPED. THE ELECTRICAL ODOR STILL VERY STRONG DECLARED EMERGENCY. RETURNED TO DEPARTURE, LANDED WITHOUT INCIDENT. PERFORMED VISUAL INSP OF FLOOR COMPONENTS. PERFORMED OPS CHECK, UNABLE TO DUPLICATE. TEST FLIGHT SATISFACTORY.