  We re-examine the puzzling $\pi^+$ emission from the weak decay of
$^4_\Lambda$He and propose an explanation in terms of a three-body decay of the
virtual $\Sigma^+$. Such a resolution of the $\pi^+$ decay puzzle is consistent
with the calculated $\Sigma^+$ probability in light $\Lambda$ hypernuclei as
well as the experimentally observed $\pi^+$ energy spectrum and $s$--wave
angular distribution.
