The spectral up-down asymmetry of type 1 echoes returned from the equatorial electrojet irregularities is shown to be a consequence of the nonlinear development of the horizontally propagating large scale primary waves which dominate the k spectrum of the electrojet turbulence. The waves reduce the vertical electric polarization field of the electrojet and suffer second harmonic distortion as they grow. These effects together could cause an asymmetry exceeding 20% between the upward and downward components of the relative (to the ions) electron velocity associated with the primary waves. This asymmetry, which changes its direction from day to night as does the horizontal electrojet current, could easily account for the radar observations. The modification of the vertical polarization field also limits the perturbed vertical electron velocity to a value about the same as the mean horizontal electron velocity, which should explain why type 1 echoes are observed in all directions only when the mean electron velocity is supersonic. Finally, this modification of the polarization field amounts to a significant reduction in the electrojet conductivity, an effect which should be included in electrojet models.