  Contributions of flavour-changing neutral currents in the 3 3 1 model with
right-handed neutrinos to mass difference of the neutral meson system $\Delta
m_P (P = K, D, B)$ are calculated. Using the Fritzsch anzats on quark mixing,
we show that the third family should be different from the first two. We obtain
a lower bound on mass of the new heavy neutral gauge boson as 1.02 TeV.
