With only wing tanks containing fuel, the engine start is accomplished with (main)tank to engine.
Fuel panel configuration : All main tank boost pumps on and X-feed vlv's 1 & 4 open and 2 & 3 closed.
With wing tanks full and when center wing tank also contains fuel (more than 1800 kgs) the start is made with engines 1 & 4 fed by center wing tank, with both CW
override jettison pumps selected on and overriding the main tank 1 &4 boostpumps.
Fuel panel configuration : All main tank boost pumps on, both CW
overr/jett pumps on, X-feed vlv's 1 &4 open and 2 & 3 closed.
Ref : 747 OM
part B ,normal procedures, 18.104.22.168.
Operating a twin over the ocean, you're always one engine failure from a total emergency.