To determine definitely the transient characteristics of smoke emission from a diesel engine, it is necessary to know details of its power transmission elements such as fuel injection system, combustion process, engine rotating system and its friction losses. Previous studies have been unclear about the relations between the engine performance, smoke characteristics and influence of operating conditions, especially on the two-cycle engine. Therefore, the authors carried out the experiments while changing its brake load and fuel pump rack, respectively, to examine the effects of the operating conditions on the exhaust smoke density under transient operations. (A) For the covering abstract see IRRD 865952.