C172 ABORTS TKOF WHEN 50 FT IN THE AIR AFTER ENG SURGE AND PWR LOSS. ON TAXI BACK FINDS THAT FUEL SELECTOR WAS IN OFF POS FOR 1ST TKOF AT TRI.

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I DID MY START UP CHKLIST (OR SO I THOUGHT). SET MY GPS FLT PLAN. HAD TO WAIT FOR GND TO GET TO ME BEFORE TAXI. RECEIVED CLRNC TO TAXI; READ IT BACK AND TAXIED TO RUN-UP AREA. DID A RUN-UP AND PRE-TKOF CHKLIST. HAD A GUT FEELING SOMETHING WASN'T RIGHT EVEN THOUGH ENG AND EVERYTHING ELSE CHKED OUT OK. RE-DID CHKLIST; BUT APPARENTLY TOO QUICKLY AND AGAIN; DID NOT CATCH FUEL SELECTOR VALVE. I DID NOT TOUCH IT. THE QUICK GLANCE DIDN'T CATCH IT. RECEIVED CLRNC TO TAKE OFF. THEN THE TKOF AND ABORT OCCURRENCE. PWR REDUCTION AND SURGE ON TKOF. CORRECTIVE ACTION: ANNOUNCED 'ABORTING TKOF' TO ATC AND RE-LANDED THE ACFT ON RWY. POSITIONED FUEL SELECT VALVE IN 'BOTH' POS. ENG WAS RUNNING SMOOTHLY DURING TAXI AND SUBSEQUENT RUN-UP; SO RESUMED TRIP. THERE WERE NO OTHER PROBS. WHILE TAXIING BACK AFTER THE EVENT AND A CLRNC; I STOPPED AT AN INTERSECTING RWY TO CHK FOR TFC AND GLANCED AT THE HOBBS. SUBTRACT ABOUT A MIN FROM THE .2 AND YOU HAVE ABOUT 11 MINS THAT THE ENG RAN WITH THE FUEL SELECT VALVE OFF. THAT IS AMAZING. FACTORS AFFECTING HUMAN PERFORMANCE: HAD 'EVOLVED' AWAY FROM MY FORMER PRACTICES OF: TOUCHING THE ITEM ON THE CHKLIST; IN THIS CASE; TURNING THE FUEL SELECTOR VALVE TO 'BOTH' UNLOCKING THE ACFT IN TIEDOWN AREA. TOUCHING THE ITEM ON MY PRE-TKOF CHKLIST. DID NOT PAY PROPER ATTN TO 'THAT QUEASY FEELING' OR THE CHKLIST ITEMS.