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MgB2 samples have been synthesized over a wide temperature range and from the stoichiometric and excess magnesium composition. The role of magnesium overdoping on the superconducting characteristics of MgB2 has been studied, and hence, the correlation between the critical current density, porosity, and density of the MgB2 samples has been established. The excess magnesium in the starting composition expands the synthesis temperature range over which the MgB2 phase can be synthesized and also enhances the superconducting properties in terms of Tc, ΔT, and residual resistivity ratio. The reduced weight loss due to Mg vaporization, and hence the lower porosity in the sample synthesized from the stoichiometric composition and at Ts = 900°C, reflected the higher Jc in the MgB2 sample in this series. Whereas with the excess magnesium in the starting composition, the sample with the highest Jc has been synthesized at a lower synthesis temperature of Ts = 700°C. The correlation between weight loss during heat treatment, sample density, resistivity, and active area fraction has been established for vacuum-synthesized bulk MgB2 samples.