This letter proposes an easy-to-implement blindly weighted non-coherent receiver (BWNCR) for low data rate impulse radio ultra-wideband (IR-UWB) systems operating with pulse amplitude modulated (PAM) signals. We first derive the theoretically optimal weights for the likelihood ratio test based WNCR (LRT-WNCR) in closed-form. In order to refrain the LRT-WNCR from demanding a priori knowledge of the channel and the noise variance, we further develop a low complexity receiver to accomplish the optimal weight-setting and threshold-setting in an entirely blind manner. Simulations verify that the bit error rate (BER) of the BWNCR closely approaches that of the LRT-WNCR, which is achieved with ideally known channel state information and noise variance.