C152 PLT RAN SHORT OF FUEL AND DECLARED AN EMER AFTER EXTENSIVE ATC FLT PLAN REROUTING.

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MY IFR XCOUNTRY FLT ORIGINATED FROM ISP. A STANDARD WX BRIEFING WAS RECEIVED ABOUT 30 MINS BEFORE THE FLT. THE FLT WAS PLANNED TO BE 3 HRS ENRTE WITH RIC AS THE FINAL DEST. THE AIRPLANE WAS THEN VISUALLY CHKED TO HAVE 2 FULL TANKS OF FUEL; WHICH IS EQUIVALENT TO 4 HRS OF FLT TIME AT THE CRUISING ALT PLUS A LITTLE EXTRA TO FACILITATE RUN-UP AND CLB. UPON RECEIVING CLRNC PRIOR TO THE FLT; THE ENTIRE FLT PLAN WAS RERTED VIA A DIFFERENT VICTOR AIRWAY AND VOR. THE REVISED ROUTING WAS ACCEPTED BY ME. AT A LITTLE BIT AFTER 3 HRS INTO THE FLT; I HAD DETERMINED THAT TO REACH MY RIC DEST THE FLT WOULD CONTINUE ON FOR ANOTHER 30 MINS. HENCE; RUNNING INTO THE REQUIRED NIGHT IFR FUEL RESERVES. APPROX 10 NM FROM RIC; A 'DIRECT RIC CLRNC' HAD BEEN AMENDED TO FACILITATE OTHER LNDG TFC. THEREFORE; ADDING UP EXTRA FLT TIME TO GET TO THE ARPT. THE ATC CTLRS HAD BEEN PREVIOUSLY INFORMED ABOUT THE FUEL SIT. AT ABOUT LESS THAN 5 NM TO RIC; AN EMER SIT HAD BEEN DECLARED BY ME DUE TO THE ENG RUNNING ROUGH FOR A SHORT PERIOD OF TIME. HOWEVER; PWR WAS REGAINED AND A SAFE PWR-ON LNDG WAS MADE. I WAS ABLE TO TAXI ON MY OWN PWR TO THE FBO RAMP ESCORTED BY EMER SVC VEHICLES.