  We investigate the combined effect of neutrino masses and non-standard
couplings on the various lepton spectra in $\mu$ and $\tau$ decays. We
emphasize the energy spectra of the neutrinos, which can be measured in the new
KARMEN experiment and hence will yield novel information on deviations from the
$V-A$ structure. To constrain these couplings, QED radiative corrections have
to be taken into account. We evaluated them and found small corrections to the
neutrino spectra.
