  Low energy $\pi^+$ emission in hypernuclear weak decays is studied in the
soft pion limit. It is found that the $\pi^+$ decay amplitude is dominated by
the $\Delta I=3/2$ part of nonmesonic weak decays according to the soft pion
theorem. The ratios, $R(\pi^+/soft \pi^-) $, for light hypernuclei are
estimated in the direct quark mechanism, which predicts violation of the
$\Delta I=1/2$ rule, and found to be about 1/3 for $^4_{\Lambda}He$.
