Carbynes have gained highlight due to their unique properties and applications in molecular electronics exhibiting resonant tunnel effect. We studied the electronic transport through a molecular tunnel junction composed of two polyyne-type carbynes separated by distance (4 Å ≥ d n  ≥ 2.1 Å) higher than bond length (d n  > d C-C ) ranging from 0.1 Å based on Density Functional Theory/Non-Equilibrium Green's Function (DFT/NEGF). The frontier molecular orbitals and bond lengths of the polyyne (d C-C  ≈ 1.36 Å, d C ≡C  ≈ 1.26 Å) at 0.0 V become equal to those in cumulene-type carbynes (d C= C  ≈ 1.28 Å) at 0.9 V occurring a semiconductor-metal transition for d n  < 4 Å. I-V (dI/dV-V) curve presents switching behaviour up to 0.6 V and after a diode behaviour favoured as d n decreases, that is, to 4.0 Å is 3.3 nA (5 nS) while for 2.1 Å is 3750 nA (1500 nS) showing metallic nature. The log(I)-V log(dI/dV)-V curve exhibits the behaviour for low bias voltage while the I-d n curve is exhibited for high bias voltage. The exponential expression for G(d) fits perfectly with the G max result obtained with DFT/NEGF calculations. Transition Voltage Spectroscopy (TVS) confirms rectangular barrier and direct tunneling for V d-s  < ϕ B /e playing a tunneling rule for electronic transport of these 1-D systems.