B747-400 CREW HAD CONTINUOUS STICKSHAKER AND AIRSPD IRREGULARITY ON DEP AT HKJK.

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INCIDENT RPT AT NBO ARPT; RESULTING IN RETURN FOR LNDG MAY/FRI/02. CREW MEMBERS ON BOARD: CAPT WAS PF; FO IN R SEAT PNF. ONE FO WAS JUMP SEAT SUPPORT PLT; ANOTHER FO JUMP SEAT SUPPORT PLT. ALL TKOF PREPARATIONS WERE COMPLETED UP TO FINAL FLT DECK PROC. WE INPUTTED ZFW DATA AS PER FOM INTO THE FMS. THE ZERO FUEL WT WAS 270.2 TONS AND FUEL ON BOARD 108.2. TONS. COMPLETED PUSHBACK AND TAXI. ALL CHKLISTS COMPLETE. NORMAL MAX THRUST DEP ON THE NAROK B SID RWY 6 TO FL310. DEP SPDS AS COMPUTED BY THE CREW MEMBERS V1 150; VR167; V2 177. THE FMC SPDS CONFIRMED AND ENTERED AT V1 151; VR 168; V2 179. CLRED FOR TKOF; THE ENG PARAMETERS NORMAL AND TKOF NORMAL. ON CLBOUT; ACFT WAS STABLE AT V2 +15 KTS (+/- 1 KT); THEN NOTED THAT TARGET COMMAND SPD BUG ACCELERATED ON ITS OWN ACCORD TO V2 +23 KTS AT 300 FT RA. REST OF CLBOUT NORMAL ON NAROK B SID UNTIL FLAP RETRACTION FROM POS 1 TO 'UP' AT APPROX 270 KIAS ON PFD. SPD INDICATED APPROX FLAPS UP SPD AND INCREASING; BEFORE CALLING FOR FLAPS RETRACTION. IMMEDIATELY UPON MOVEMENT OF FLAP TO 'UP;' STICKSHAKER ACTIVATED AS LOW AND HIGH SPD BUFFET MARGIN MERGED AT RAPID RATE. IMMEDIATELY CALLED FOR MAX THRUST AND FLAPS EXTENSION BACK TO POS 1. STICKSHAKER CEASED. BUFFET SPD TAPE SEPARATED TO WITHIN SAFE MARGINS FOR FLAP POS. ACFT CLBING IN LIGHT TURB IN IMC; CUMULONIMBUS IN THE VICINITY; WHEN CLR OF THE WX APPROX 3 MINS. REPEATED FLAP RETRACTION WITH SAME RESULT. NO EICAS AND NO STATUS MESSAGE DISPLAYED. ACFT AT ABOUT FL180 CLBING INTERMEDIATE LEVELOFF REQUESTED AND APPROVED. AT FL200 CREW IN CONCERN RESEARCHED QRH; PERFORMANCE DATA AND ACFT FLT MANUAL. ENGINEER WAS SUMMONED TO ASSIST IN EVALUATION OF SIT. REQUESTED RETURN TO NBO. ENRTE ACFT STABLE AND AUTOPLT ON. A LAST ATTEMPT TO RETRACT FLAPS WAS MADE WITH THE SAME RESULT. ACFT WAS CLRED TO DSND TO 12000 FT. DUE TO TERRAIN; STOPPED DSCNT AT 15000 FT. SATCOM WAS ESTABLISHED WITH DISPATCH AND MAINT. WE INFORMED THEM; OF OUR SIT TO DUMP FUEL AND LAND AT NBO IN CONCURRENCE WITH DISPATCH. FLEW INITIALLY TOWARDS GG. DUE TO WX; ELECTED TO HOLD AT NV AT 15000 FT. INITIATED FUEL DUMP PER QRH AND DECLARED EMER. DURING DUMPING; APPROX 40 MINS; MADE NUMEROUS ATTEMPTS TO CONTACT OPS ON SATCOM UNSUCCESSFULLY DUE TO PHONE NUMBER BEING 'NOT AUTH.' DUE TO ENCROACHING CUMULONIMBUS APCHING ARPT AND FUEL GRAVITY XFER VALVE PROB; RESULTING IN FUEL IMBAL; DUMPING WAS TERMINATED AND DECISION TO LAND OVERWT WAS MADE FOR TOUCHDOWN AT 305.1 TONS PER FMC WT WAS MADE. DURING DUMPING; IT WAS DISCOVERED THAT CAPT'S AND FO'S PFD INDICATED AIRSPDS WERE IN AGREEMENT. HOWEVER; THEIR INFO WAS APPROX 15 KTS HIGHER THAN THE STANDBY AIRSPD INDICATOR. BASED ON THE ABOVE INFO AND CREW ASSUMPTION BY ALL AVAILABLE INFO THAT WE WERE AT A HIGHER WT THAN PREDICTED; WE HAD A FLT COMPUTER SYS PROB. A VREF SPD WAS MANUALLY CALCULATED BASED ON CURRENT CONDITION. LNDG WAS ACCOMPLISHED AT FLAPS 30 DEGS. ACFT RETURNED TO APRON; ALL CHKLIST PROCS ACCOMPLISHED. ACFT SECURED; THE CREW DEPARTED TO THE HOTEL.