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Effects of residual carbon on the carrier-doping level and resulting superconducting properties were systematically investigated for Y123 melt-solidified bulks containing different amounts of carbon. The dependence of Tc on annealing temperature in flowing oxygen was almost identical among each sample from underdoped to optimally doped state and all the samples exhibited highest Tc when they were annealed at ~500degC. On the other hand, the carbon-free samples showed apparently lower Tc than those of the carbon containing samples in the overdoped state. Especially, a sample fabricated in air showed the quite small decrease in Tc by overdoping, suggesting that residual carbon suppresses effective carrier doping to be heavily overdoped state for Y123 melt-solidified bulks. Therefore, Y123 melt solidified bulk with less residual carbon exhibited higher Hirr and Jc properties at the overdoped state.