Excitation functions of the reaction products were measured for the reactions induced by 4,6He projectiles on 208,206Pb targets, leading to the same compound nucleus. The excitation functions for the 2n evaporation channels were obtained at energies below the sub-Coulomb barrier region. A large value of the fusion cross section was observed in the case of the reaction induced by the weakly bound 6He projectile. This reflects an unusual mechanism is present in reactions induced by weakly bound nuclei.
