What was found
PDX FLT NR 2040, ON ENGINE START OF NR 2 ENG AND AFTER SELECTING NR 2 BLEED ON, F/A AND FLT DECK CREW NOTICED SMOKE IN CABIN AND COCKPIT. ABORTED THE START ASSUMING EXHAUST MAY HAVE ENTERED WITH TAIL WIND AND GAVE SECOND START ATTEMPT. LEFT THE NR 2 BLEED OFF FOR ABOUT 30 SECONDS AND NO SMOKE APPEARED UNTIL SELECTED THE NR 2 BLEED ON. ABORTED AND SHUTDOWN NR 2 ENGINE. AFTER DEPLANING TRIED A 3RD START WITH BLEEDS OFF. THEN SELECTED NR 1 BLEED ON AFTER NR 1 ENGINE START AND NO SMOKE. MAINTENANCE COMPLIED WITH BOMBARDIER SERVICE LETTER DH8-SL-21-027. GROUND RAN NR 2 ENGINE WITH BLEED ON AT VARIOUS TEMP SETTINGS FOR 40 MINUTES. NO ABNORMAL ODORS NOTED. NO PARTS REPLACED. AIRCRAFT RETURNED TO SERVICE.