A D328 CREW; WHILE PUSHING BACK AFTER ENG START AT BOS; EXPERIENCED SMOKE IN THE CABIN AND COCKPIT.

Narrative

WE PUSHED BACK FROM THE GATE IN BOS AND COMPLETED THE BEFORE START CHKLIST. WE THEN STARTED THE #2 ENG WHICH STARTED NORMALLY. WHEN THE PUSHBACK WAS COMPLETE; WE SET THE PARKING BRAKE AND THE GND CREW DISCONNECTED THE TOW BAR. ONCE THEY WERE CLR; WE STARTED THE #1 ENG. THE START WAS NORMAL BUT PRIOR TO BEGINNING THE AFTER START FLOWS AND CHKLIST; WE SMELLED SMOKE IN THE COCKPIT. THE FLT ATTENDANT CONTACTED US AND NOTICED THE SMELL IN THE CABIN. A THIN HAZE BECAME VISIBLE. I IMMEDIATELY SHUT DOWN BOTH ENGS AND WAITED A MOMENT TO SEE IF THE SMOKE WOULD CLR. IT DID; SO WE CONTACTED OPS AND HAD THEM TOW US BACK TO THE GATE. NO EMER WAS DECLARED AND WE DID NOT EVAC THE ACFT. THE FO THOUGHT THE SMELL WAS FROM BURNING ELECTRICAL EQUIP. I COULDN'T DISTINGUISH THE ODOR AND MAINT FOUND NO MALFUNCTION. I WAS CONCERNED THAT EXHAUST MAY HAVE BEEN DIRECTED INTO THE CABIN BY THE PACKS; BUT THEY WERE SELECTED OFF PER THE BEFORE START CHKLIST. I LOOKED UP AT THE OVERHEAD PANEL AFTER THE ENGS WERE SHUT DOWN AND THEY WERE SELECTED OFF SO I DON'T KNOW WHAT THE CAUSE MAY HAVE BEEN. AS A PRECAUTION; WE SHUT DOWN AND RETURNED TO THE GATE.