A two-stroke internal combustion engine has at least one cylinder having a bore diameter, a piston slip-fit in the cylinder, the piston having an upper portion and a lower portion and a central portion of significantly less than the bore diameter, providing an annular space between the central portion and the cylinder wall, and an air pump providing air to one or more intake ports, wherein for a significant portion of every stroke both one or more exhaust ports and the one or more intake ports are open to the annular space between the central piston portion and the cylinder wall, allowing the air pump to force air from the one or more intake ports around the central piston portion to the one or more exhaust ports.