CASE OF ROTARY DISC-VALVE INLET PORT ENGINE THE OUTPUT CHARACTERISTICS of two-stroke cycle engines are determined mainly by the charging efficiency which is a product of the delivery ratio and the trapping efficiency. With the same scavenging system, there i s little difference in trapping efficiency at a specified delivery ratio. (1)" Therefore, the output characteristics of crankcase-scavenged two-stroke cycle engines with the same scavenging system depend chiefly on the delivery ratio. When these engines are used as prime movers of motorscooters or auromobiles, it is usually not required to have the tuning effects from the inlet and/or exhaust pipe sysrems because of their vehicle characteristics. Under these "Numbers in parentheses designate References at end of Part 1.