The bio-diesel is the best replacement of diesel fuel for rural agricultural areas at less cost. But the improper combustion of bio-diesel inside the engine cylinder due to inaccurate spray characterization is the cause of low performance level of engine. It is essential to change the spray characterization when we use bio-diesel in place of conventional diesel fuel. To modify the spray characterization is not an easy and suitable task high level research is required for the same but by simply changing the injector hole diameter we can obtain the optimum values of performance characteristics. By the use of ceramic coating on piston its reduces the heat loss from cylinder and due to that reduction in heat loss proper combustion of bio diesel can obtain even after increasing the injector hole diameter.In this work both changing the injector diameter hole with stable ceramic coating (0.3mm) has been done and experimentally find out the optimum values of performance characteristics of engine using karinja oil blends as a fuel.