Yep, just as slappy said, it's from the rest position. It's not just the opening of the carbs that's starting the movement, there's taking up any slack, then cable outer movement, as it tries to straighten itself out, plus a few more tiny bits of slack here there and everywhere built in to avoid the jamming of the throttle.
I sort out as much slack as I can get away with at the carbs end, tweak it with the mid cable adjuster, them fine tune it with the engine running. Just about gets it spot on.
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