NMRA CV 2 - Vstart (Start Volts)
CV 2 Adds an offset voltage to the motor so that the locomotive starts moving at a faster speed. This is useful for speed matching or for locomotives without BEMF. this setting is also useful for inefficient electric motors which have require a higher voltage to overcome "stall current." Some motors may lurch or repeatedly stop and start if the start volts are too low. Increasing the start volts can improve performance by increasing the low-end power. Vstart is also referred to as "boost" by some manufacturers.
Excerpt from S-9.2.2 of the NMRA Standards and Recommended Practices:
"Vstart is used to define the voltage drive level used as the start voltage on the motor. The voltage drive levels shall correspond linearly to the voltage applied to the motor at speed step one, as a fraction of available rectified supply voltage. When the voltage drive level is equal to zero, there shall be zero voltage applied to the motor. When it is at maximum (255), the full available rectified voltage shall be applied."