Abstract: A variable volume transfer duct for maintaining an optimum volume of buffer gas in the transfer duct of a two-stroke engine during operation in order to minimize short circuit loss of fresh charge at all load levels during engine operation. The variable volume transfer duct that has two pieces, a top and a bottom duct wherein the bottom duct is aligned with and slidably disposed within the upper duct. Control means are provided for raising and lowering of the bottom duct to vary the transfer duct volume accordingly. A control means controls recirculates exhaust gas, or the secondary air, as buffer gas that fills the top of the transfer passage and regulates the buffer gas according to engine load conditions such that it provides a larger amount at higher loads and a lesser quantity at lighter loads.