The yen weakened to new multidecade lows, as more major investors joined the fray to bet against Japan's currency. + The yen was on course to notch its weakest settle since late 1986, surpassing a 1990 level of about 160.15 yen per dollar, FactSet data showed. Asset managers have amassed the biggest net short position, or bet against, the yen in at least 18 years, data from the Commodity Futures Trading Commission showed.