It is well known that the operation of dual fuel engines at lower loads suffers from lower thermal efficiency and higher unburned percentages of fuel. To improve this problem, tests have been conducted on a special single cylinder compression ignition research engine (Ricardo E6) to investigate the effect of injection timing of pilot fuel on the performance of an indirect Diesel engine fueled with gaseous fuel. Diesel fuel was used as the pilot fuel, and methane or propane was used as the main fuel which is inducted in the intake manifold to be mixed with the intake air. Through the experimental investigations, it is shown that the low efficiency and poor emissions at light loads can be improved significantly by advancing the injection timing of the pilot fuel.