In the present work experiments were done on a modified LPG Diesel dual fuel engine with diesel as primary fuel and liquefied petroleum gas as secondary fuel by providing a venturi at the inlet manifold for better performance at all loading conditions. The engine was run at different operating conditions and in each case the optimum combination fuel energy proportions were determined for best efficiency. The exhaust smoke level, temperature, and other emission parameters were measured. The results were compared with the performance of the engine with diesel as sole fuel, and as dual engine without modifications and specific conclusions were then arrived. It was concluded that the brake thermal efficiency slightly reduces with modified design in comparison with conventional design. Diesel consumption is reduced considerably and also CO and HC emission are slightly higher at lower loads and reduces with increase in load. Smoke density and NOx are reasonably reduced in the modified design with LPG flow rate of 0.3 kg/hr found to be optimum in all conditions.