AN MD80 FLC EXPERIENCED CTL PROBS AFTER LIFT-OFF AS A RESULT OF A FUEL IMBALANCE. THE L WING HELD 4000 LBS MORE THAN THE R WING. THE IMBALANCE WAS CAUSED BY THE FAILURE TO CLOSE THE DEFUEL VALVE AND DOOR AFTER DEFUELING. FLAP AND SLAT POS CONTRIBUTED TO THE FAILURE TO RECOGNIZE THAT THE DOOR WAS OPEN.

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DUE TO ICE AND SNOW AT SYR WE NEEDED TO REDUCE WT FOR TKOF. WE NEEDED TO OFF-LOAD 7200 LBS. DISPATCH ELECTED TO OFF-LOAD FUEL AND MAKE AN ENRTE FUEL STOP AT DTW IN ORDER TO ACCOMMODATE A FULL PAX LOAD. FUELER AT SYR HAD US TRANSFER FUEL FROM WING TANKS TO CTR SO HE COULD DEFUEL. I CLOSED THE XFEED VALVE WHICH WAS CONFIRMED BY THE FO; WHEN DEFUEL WAS COMPLETED. IMMEDIATELY AT LIFT-OFF THE L WING WAS VERY HVY NEEDING ABOUT 60 WHEELTHROW FOR LEVEL FLT. I SAW A FUEL IMBALANCE OF 4000 LBS IN THE WING TANKS AND 3300 LBS IN THE CTR TANK. THE CTR TANK HAD BEEN EMPTY AT THE GATE. I OPENED THE XFEED AND FED BOTH ENGS FROM THE L TANK. I WAS ABLE TO BAL THE FUEL LOAD FOR LNDG. AT DTW THE FUELER CONFIRMED THAT THE DEFUEL VALVE AND DOOR HAD BEEN LEFT OPEN. THE FUELER MISSED CLOSING THE VALVE AND DOOR AT SYR AFTER DEFUELING. A POSSIBLE REASON FOR HIS MISSING THE VALVE WAS THE FLAPS AND SLATS WERE LEFT DOWN AT THE GATE DUE TO LNDG ON SNOW AND ICE. DURING THE BEFORE STARTING ENGS CHKLIST AT THE GATE I NOTED THE PROPER FUEL AND DISTRIBUTION AND THE XFEED VALVED WAS CLOSED. DUE TO NIGHT TAXI AT AN UNFAMILIAR ARPT ON ICE AND SNOW I FAILED TO DETECT THE FUEL IMBALANCE PRIOR TO TKOF. HAD OUR TKOF BEEN DELAYED 5-10 MINS LONGER THE ACFT MIGHT NOT HAVE BEEN CONTROLLABLE AFTER LIFT-OFF. WE SHOULD ENCOURAGE ALL CREWS TO CHK FUEL BALANCE PRIOR TO TAKING THE RWY.