We present the results of an analysis of time-resolved spectroscopy of V617 Sgr, the Wolf-Rayet star WR 109, in the Hβ and He II lambda4686 region. Radial velocity curves were obtained confirming the orbital period of 4.97 hr found from photometric observations. These curves indicate that the superior conjunction of the line-forming region occurs close to the primary eclipse. Constraints on the stellar masses in this peculiar binary are derived from the emission lines. The orbital behavior of the emission line profiles is analyzed in detail. A Doppler tomography study of the Hβ and He II lambda4686 lines is performed, aiming to estimate the locus of line formation in the system. The observations may suggest the presence of an optically thick wind. An extended emission region consistent with a hot spot and free-falling gas is also inferred from our analysis. The observed characteristics, such as the strong intensity of He II lambda4686 (He II/Hβ flux ratio ~2.9) and the presence of emission lines of highly ionized elements like N V and O VI, are not usually seen in normal cataclysmic variables and, in this respect, V617 Sgr is quite similar to the star V Sge.