A low angular momentum (sub-Keplerian) and a low viscosity flow produce a standing shock (boundary layer of the Compton cloud) during the outburst of a transient black hole candidate (BHC). In progressive days, as cooling rate increases, the average shock location moves inward to satisfy the Rankine-Hugoniot condition during the rising phase. Because of the resonance between cooling and infall time scale, the shock oscillates, producing low frequency Quasi Periodic Oscillations (QPOs) of monotonically increasing frequency. An exactly opposite situation prevails during the declining phase. The geometry of the Compton cloud also dictates the spectral states. Thus the QPOs, the spectral states, and the formation of the shock itself are linked to viscosity of the sub-Keplerian flow. We analyze the data of a few BHCs and calculate their Keplerian (αK) and sub-Keplerian (αSK ) component viscosity parameters during the rising and the declining phases of the outburst. We find that the viscosity profile changes monotonically in a similar way for all the outbursting candidates during their evolution. We estimate the range of the sub-Keplerian viscosity parameter which is required to trigger different spectral states. From our study, we infer that the typical range of αSK parameter of the sub-Keplerian flow is within 0.1 for the transient sources. Most importantly our calculated αK of these sources is well above αSK , which makes the analysis consistent. The fitted parameters also help us to study the decay of the lightcurve and give us the idea of amount of disc viscosity is needed to get the observed decay.