OFF ARPT EMER FORCED LNDG DUE TO FUEL EXHAUSTION.

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THE FLT ORIGINATED IN NEPHI; UT. A VFR FLT PLAN WAS FILED FOR A 3.5 HR FLT TO LAS VEGAS; NV. THE FUEL TANKS WERE TOPPED OFF IN NEPHI 1 HR BEFORE TKOF. CRUISE ALT WAS 8500 FT; WHICH WOULD MEAN A 4.22 HR ENDURANCE ACCORDING TO THE ACFT FLT MANUAL. THE FLT LASTED 3.5 HRS AT WHICH TIME THE ENG QUIT ON FINAL APCH TO RWY 25 AT N LAS VEGAS ARPT. AN EMER WAS DECLARED AND THE ACFT WAS SAFELY LANDED ON A DIRT ROAD 1 MI FROM THE RWY. I BELIEVE THE CAUSE OF THE PROB WAS TWOFOLD: NOT TAKING INTO ACCOUNT THE EFFECT OF A HOT DAY ON FUEL EXPANSION AND EVAPORATION ESPECIALLY ON AUTO GAS WHICH WAS USED IN THE AIRPLANE AND INCORRECT LEANING OF THE ENG. BECAUSE IT WAS A HOT DAY AND THE ENG OIL WAS READING A HIGHER TEMP THAN NORMAL; THE MIXTURE WAS SET RICHER THAN NORMAL TO HELP IN COOLING THE ENG. SINCE THE ACFT FLT MANUAL LISTS THE ENDURANCE FIGURES WITH A LEAN MIXTURE; I SHOULD HAVE TAKEN INTO ACCOUNT THIS FACT AND REDUCED THE ENDURANCE TO REFLECT THE RICHER MIXTURE. THE R FUEL GAUGE WAS READING EMPTY; BUT THE L GAUGE SHOWED NEARLY 1/4 OF A TANK; LEADING ME TO FURTHER BELIEVE I WOULD HAVE PLENTY OF FUEL TO FINISH THE FLT.