B737-700 FLT CREW HAS A CONFIGN WARNING DURING TKOF ROLL AT LAS.

Narrative

WE WERE TAXIING FOR TKOF ON RWY 1R LAS. WE WERE ON TXWY D AND I SWITCHED TO THE TWR FREQ. THE TWR CTLR CLRED US FOR TKOF AND TOLD US TO FLY HDG 315 DEGS AFTER DEP. I WAS BUSY COMPLETING MY FLOW AND TALKING TO ATC AND I DO NOT RECALL IF THE CAPT DID THE THRUST LEVER CHK OR NOT. WE COMPLETED THE BEFORE TKOF CHKLIST. THE ACFT WAS POSITIONED ONTO THE RWY AND THE CAPT GAVE ME CTL. I ADVANCED THE THRUST LEVERS AND WE RECEIVED THE TKOF WARNING HORN. THE CAPT IMMEDIATELY TOOK CTL OF THE ACFT WHICH HAD BARELY STARTED ROLLING AND REJECTED THE TKOF. I NOTIFIED ATC AND WE TAXIED CLR OF THE RWY. WE COMPLETED OUR CHKLISTS AND THEN WENT ON TO DIAGNOSE THE PROB. THE ACFT WAS PROPERLY CONFIGURED FOR TKOF (IE; TRIM; FLAPS; ETC). THE CAPT AND I BOTH CHKED THE SPD BRAKE LEVER AND IT WAS IN THE DOWN DETENT. THE CAPT DID NUMEROUS THRUST LEVER CHKS TO SEE IF WE COULD GET THE TKOF WARNING HORN WHICH WE DID EACH TIME. HE CHKED THE SPD BRAKE LEVER NO LESS THAN 3 DIFFERENT TIMES WITH HIS HAND THAT IT WAS IN THE DOWN DETENT. WE STILL RECEIVED THE TKOF WARNING HORN. THE CAPT DECIDED TO GATE RETURN. UPON RETURNING TO THE GATE; MAINT DETERMINED THE PROB TO BE DUST BUILD UP IN THE SWITCH AREA OF THE SPD BRAKE LEVER. THEY CLEANED THE AREA AND THE THRUST LEVER CHK WAS NORMAL. THE LOGBOOK WAS SIGNED OFF AND WE CONTINUED ON. THE CAPT NEEDS TO DO THE THRUST LEVER CHK. I NEED TO BE POSITIVE THAT I HAVE WITNESSED THE COMPLETION OF THE THRUST LEVER CHK.