A B747-400 PERFORMS A REDUCED THRUST TKOF AT LAX. CREW SENSES A PERFORMANCE THAT IS LESS THAN EXPECTED AND FINDS THAT THERE MAY HAVE BEEN AN ERROR COMMITTED IN INSERTING THE TKOF WTS IN THE FMC; THEREBY SETTING THE THRUST COMPUTER RESPONSES TO A SETTING TOO LOW FOR THE PROJECTED TKOF WT.

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NORMAL PREPARATION FOR DEP WITH SLIGHTLY MORE THAN USUAL ACTIVITIES IN COCKPIT; PURSER HAD CONCERNS ABOUT 2 ELDERLY PAX. TAXI OUT NORMAL EXCEPT A LONGER THAN NORMAL WAIT FOR FINAL WTS. JUST PRIOR TO TAKING THE RWY; RECEIVED A CALL FROM THE COMPANY THAT THEY HAD MADE AN ERROR IN FINAL WTS AND WOULD SEND US A REVISION. IN APPROX 4 OR 5 MINS; WE RECEIVED NEW WTS APPROX 10000 LBS LOWER. NUMBERS INSERTED INTO FMC AND TKOF CHKLIST COMPLETED. ON TKOF; ACCELERATION APPEARED LESS THAN NORMAL (TKOF PWR AT REDUCED SETTING). HOWEVER; THE ACCELERATION GREEN ARROW INDICATED SUBSTANDARD ACCELERATION. THIS RATE DECREASED AS ACFT APCHED V1 -- ROTATED AT VR APPROX 1500-1800 FT FROM END OF RWY 25R. CLBOUT WAS BELOW NORMAL PERFORMANCE. RELIEF FO INSTRUCTED TO CALL LOAD PLANNING TO CONFIRM WTS. HE RESPONDED THAT THE PROB OCCURRED BECAUSE THE TKOF PWR WAS NOT SET PROPERLY IN THE FMC. PAGE WAS SELECTED TO CONFIRM; BUT DATA DROPS OUT ONCE AIRBORNE. HOWEVER; ACFT WAS NOW IN CLB CONFIGN AND FMC SELECTED TO CLB TWO PWR -- INDICATING THAT THE FMC HAD EITHER BEEN PROGRAMMED WRONG OR HAD SOME OTHER IRREGULARITY. BOTTOM LINE IS 4 PLTS OVERLOOKED AN IMPROPER PWR SETTING FOR TKOF. TOO MUCH RELIANCE ON THE MACHINE FOR NORMAL OPS. THE OLD MANUAL FLIP CARDS WOULD HAVE PREVENTED THIS SIT; OR THE FMC SHOULD VERIFY THE INTERACTION BTWN PAGE INFO TO PREVENT ERRORS.