The Bank of Japan is far from done driving down the yen if it wants to secure a 2 percent inflation target next year, a survey of economists by Bloomberg shows.

The median estimate of 27 economists in a survey carried out between last Thursday and Tuesday shows that the yen needs to fall to 140 per dollar, a level last seen in 1998, to help the central bank meet its goal.

Even after a 23 percent decline since BOJ Gov. Haruhiko Kuroda began record monetary stimulus, that means a further 13 percent drop from the current level.