All reciprocating (piston) engines are basically air pumps. The characteristics of a two cycle engine allow you to run it on compressed air. You hook an air hose to the spark plug hole, feed it with a steady supply of compressed air, pull the starter cord and the engine will run on the compressed air. The pressurized air is taking the place of the explosion of fuel/air to push the piston down. A two cycle engine exhausts every time the piston goes down which is why the compressed air can be used to run it. When I check a two cycle motor with air, I stick a rubber blow gun tip into the spark plug hole and hold it there. I don't run it for hours, just a minute or so in order to test the ignition for spark output and make sure there are no problems with piston and rings. It's not rocket surgery. 8-)
TDD