PLT OF C172 ENCOUNTERED FUEL EXHAUSTION NEAR DEST ARPT. LANDED UNDER EMER CONDITIONS WITH INTERMITTENT PWR LOSS.

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ON FEB/WED/03; DURING A RETURN FLT FROM OAK TO FAT; THE AIRPLANE I WAS FLYING BEGAN TO RUN OUT OF FUEL. ULTIMATELY; I DECLARED AN EMER AND WAS CLRED TO LAND. CONTRIBUTING FACTORS -- FAULTY FUEL GAUGES AND SENSORS AS DETERMINED BY THE MECHS; POSSIBLE VISUAL INSPECTION OF THE FULLNESS OF THE TANKS; PERCENTAGE OF PWR CHART NOT PART OF THE POH -- PROBABLY DUE TO STC SA 703GL; AND INSTALLATION OF LARGER 180 HP ENG. BEFORE THE ROUND-TRIP FLT FROM FAT TO OAK BEGAN; I OBTAINED A WX BRIEFING AND PREPARED A FLT PLAN BASED ON THE PERFORMANCE CHARTS IN THE POH. I DETERMINED I WOULD NEED 37 GALLONS OF FUEL FOR THE FLT; INCLUDING TAXI; TKOF; CLB; CRUISE; AND RESERVE. THE TANKS HOLD 40 GALLONS USABLE AND 43 INCLUDING UNUSABLE; SO I FIGURED FULL TANKS WOULD HOLD MORE THAN ENOUGH. IT WAS NOT. DURING MY PREFLT INSPECTION; FUEL GAUGES READ BEYOND FULL AND A VISUAL INSPECTION AGREED. MY FIRST INDICATION OF THE PROB (A LOSS OF PWR); OCCURRED APPROX 3 HRS AND 10 MINS OF HOBBS TIME; APPROX 8 MI FROM FAT. LOOKING FOR A SOLUTION; NOT KNOWING FUEL EXHAUSTION WAS THE PROB; I APPLIED CARB HEAT; WHICH BROUGHT THE PWR BACK. I SCANNED MY GAUGES AND VIEWED 1/4 TANK OF FUEL ON THE L AND EMPTY ON THE R. SOON THEREAFTER (APPROX 2 MINS AFTER APPLYING CARB HEAT); THE ENG BEGAN FALTERING AGAIN. I IMMEDIATELY SWITCHED THE FUEL SELECTOR FROM 'BOTH' TO 'L' AND REGAINED PWR FOR ANOTHER 2 MINS AFTER WHICH THE ENG QUIT ONCE MORE. I DECLARED MY EMER AND WAS CLRED TO LAND; AND LANDED ON RWY 11R (29L IN USE). THE ENG REGAINED PWR ON FINAL; AND I WAS ABLE TO TAXI TO PARKING UNDER MY OWN PWR. AFTER A BRIEF EXPLANATION OF WHAT HAPPENED TO THE TWR (THEY WERE VERY HELPFUL); I CHKED THE FUEL GAUGES; LEFT 1/4 TANK; R WAS EMPTY. I ADVISED THE MECHS OF WHAT HAD HAPPENED; AND THEY SUGGESTED I FILL THE TANKS TO DETERMINE IF ANY FUEL WAS LEFT. THE TANKS TOOK 43.3 GALLONS. THE MECHS THEN CHKED THE GAUGES AND SENSORS AND FOUND THEM FAULTY AND SENT THEM OUT TO BE OVERHAULED. ALTHOUGH THE GAUGES AND SENSORS WERE FAULTY; I AM STILL CONCERNED THAT I HAD FULL TANKS; BUT ONLY ABLE TO FLY 3.3 HRS OF HOBBS TIME. DURING A DISCUSSION WITH THE LINE FUELERS; THEY SAID THAT SMALL CESSNAS HAVE LONG SHALLOW TANKS; AND DETERMINING FULLNESS CAN BE DIFFICULT. WHAT MAY APPEAR TO BE FULL MAY; IN FACT; MAYBE 4-5 GALLONS SHY. THIS WOULD ONLY ACCOUNT FOR 1/2 OF FUEL. THE OTHER CONCERN I HAVE IS THE POH AND ITS PERFORMANCE SECTION FOR THE INSTALLATION OF A DIFFERENT/LARGER ENG. THE CHART USED TO DETERMINE HOW TO SET PERCENTAGE OF PWR WAS NOT INCLUDED WITH THE STC SA 703GL. THIS MAY HAVE BEEN A CONTRIBUTING FACTOR. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: ANALYST GAINED NO SUBSTANTIVE ADDITIONAL INFO AS A RESULT OF THE CALLBACK. SOME CLARIFICATION OF QUESTIONS RESULTING FROM RPTR'S NARRATIVE WERE OBTAINED AND INCORPORATED INTO THE ANALYSIS AND DIAGNOSIS SECTIONS.