F100 PIC ELECTS TO RETURN LAND AT LGA WHEN A FUEL IMBAL NOTED WAS NOT CORRECTABLE. THE CIRCUIT BREAKER FOR THE XFEED WAS POPPED AND; AFTER 1 RESET; POPPED AGAIN. THE FUEL IMBAL CONTINUED TO INCREASE SO HE WISELY CHOSE TO DECLARE AN EMER TO EXPEDITE HIS RETURN TO LGA. HE WAS 60 MI FROM THE DEP ARPT.

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FREQ: 132.17. ALT: FL200. ATC FACILITY: ZNY. LOCATION: J95 BTWN GAYEL AND STOMP APPROX 60 MI WNW OF LGA. CLBING OUT OF LGA; NOTICED FUEL IMBAL BTWN R AND L WING TANK OF APPROX 350 LBS. ATTEMPTED XFEED. FLOW BAR WOULD NOT ILLUMINATE INDICATING NO XFEED CAPABILITY. CHKED CIRCUIT BREAKERS AND FOUND FUEL XFEED CIRCUIT BREAKER POPPED. RESET ONCE; BUT POPPED AGAIN. FUEL IMBAL CONTINUED TO INCREASE. TURNED BACK FOR LGA AND DECLARED EMER TO EXPEDITE OUR RETURN. LANDED UNEVENTFULLY WITH AN IMBAL OF APPROX 1500 LBS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR SAID THAT THE ALLOWABLE IMBAL WAS 2200 LBS; DIFFERENTIAL UPON LNDG WAS 1500 LBS. HE HAD ATTEMPTED TO USE DIFFERENTIAL PWR; LESS PWR ON THE L ENG; BUT THE FUEL ON THE R SIDE STILL DEPLETED FASTER THAN THE FUEL ON THE L SIDE. RPTR SUSPECTS A FORM OF FUEL MIGRATION HAD OCCURRED WITH A PARTIALLY OPENED FUEL XFEED VALVE. MAINT APPEARED TO HAVE BEEN SATISFIED THAT THEIR CHANGING THE XFEED VALVE AND THE CIRCUIT BREAKER HAD SOLVED THIS FUEL FEED PROB.