SMA ON XCOUNTRY HAS ENG SPUTTER. DECLARES EMER AND LANDS.

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I FLEW AN SMA MANY WKENDS AT A SMALL GRASS STRIP AS AN AIR RIDE PLT. WE FLEW UNTIL WE NEEDED GAS; AND THAT WAS DETERMINED BY LOOKING IN THE TASK. I FELT I KNEW A LOT ABOUT FUEL QUANTITY N THE SMA FROM HAVING LOOKED IN THE TANKS SO OFTEN. ON THE DAY IN QUESTION; I PLANNED A FLT FROM EGLIN AFB (VPS) IN FLORIDA; TO ALEXANDRIA-ESLER FIELD (ESF) IN LOUISIANA; AS A FIRST TRIP LEG TO FORT WORTH; TX. I NOTED THE TANKS WERE NOT FILLED TO TOUCHING THE FILLER NECK; BUT DID NOT APPEAR TO ME TO BE MORE THAN 1 INCH LOW. I REMEMBER THINKING ABOUT THE SIT; BUT ONLY 1 INCH DID NOT SEEM SIGNIFICANT. I ALSO EXPECTED TO HAVE AN HR PLUS FUEL REMAINING AT DEST; AND CERTAINLY DIDN'T FEEL THE '1 INCH LOW' WOULD BE SIGNIFICANT. AS IT TURNED OUT; NEARING ESF ARPT IN LOUISIANA; I NOTED THAT THE L FUEL TANK APPEARED LOWER THAN THE R TANK. I SWITCHED TO THE R TANK; AND SHORTLY THEREAFTER THE ENG SPUTTERED 1 TIME. I IMMEDIATELY WENT BACK TO BOTH TANKS AND THE ENG CHURNED ON. WE WERE GETTING READY TO SET UP FOR THE FINAL APCH; AND WERE TRANSITIONING FROM VOR TRACKING TO VISUAL FOR LNDG AT THE TIME. WHEN THE ENG SPUTTERED; I REQUESTED IMMEDIATE VECTORS TO THE RWY FROM ATC. THEY ASKED IF I WANTED TO DECLARE AN EMER. I'VE ALWAYS READ THAT MANY PEOPLE WAIT TOO LONG TO DECLARE AN EMER; SO I SAID YES TO THE CTLR'S INQUIRY. HE GAVE ME VECTORS TO THE RWY; AND WE WERE DOWN WITH NO PROBS IN 5-8 MINS WOULD BE MY GUESS. HUMAN FACTORS: 1) DON'T THINK YOU KNOW IT ALL. IF THERE'S ANY QUESTION AT ALL; CHK IT OUT. 2) I AM CERTAINLY GLAD THAT I WAS CAREFUL AND DELIBERATE IN LEANING THE FUEL MIXTURE ABOVE 3000 FT AS RECOMMENDED. 3) MY REACTION TO THE ENG SPUTTERING TO CHANGE THE FUEL SELECTOR BACK WAS IMMEDIATE; ALTHOUGH I'D NEVER HAD THIS HAPPEN TO ME BEFORE. 4) THERE WAS NO HASTE OR RUSH TO DEPART ON THE TRIP. I SHOULD NOT HAVE TRUSTED MY 'JUDGEMENT' REGARDING THE FUEL LOAD. TO CORRECT THE SIT AND/OR PREVENT SIMILAR OCCURRENCES: 1) QUESTION ANYTHING THAT CAUSES YOU TO THINK 'IS IT OK OR NOT.' 2) LOOK FOR MORE INFO ON THE SUBJECT TO CONFIRM A DECISION. 3) KNOW YOUR ACFT.