What was found
PILOT WRITE UP ON ROTATION GREY/BLACK SMOKE FILLED CABIN. RETURN TO LAND. INSPECTED - CLEANED ACM WATER SEPARATOR SOCK. PERFORMED GROUND RUNS. NO FAULTS FOUND. AIRCRAFT WAS TEST FLOWN FOR .6 HOUR WITH NO RECURRENCE OF SMOKE. INVESTIGATION REVEALED THAT AIRCRAFT HAD TWO OCCURRENCES OF THE RIGHT ENGINE FAILING TO START DUE TO IGNITION FAULTS RECENTLY, ONCE ON 4/19 AND ONCE ON 4/20. THE IGNITION FAULTS WERE CORRECTED AND THE ENGINE WAS STARTED AND GROUND RUN NORMALLY. BOTH FAILURES TO START FLOODED THE ENGINE WITH FUEL WHICH ALSO CONTAMINATED THE ENVIRONMENTAL SYSTEM. THIS CAUSE SMOKE TO BE PRODUCED WHEN THE ENGINE WAS BROUGHT TO HIGH POWER FOR THE TAKEOFF AND THE BLEED AIR RAISED THE TEMPERATURE OF THE ENVIRONMENTAL SYSTEM.