The statement was made about using the air pump in impound. I answered, in my limited experience, that we cannot use the air pump because as the piston runs through the stroke cycle ports in the cylinder are uncovered and will leak air to the crankcase. I raced two stroke karts and this is how I remember the engines. Anyway, if air is leaked through the ports in the cylinder you do not get an accurate measurement of cylinder volumn.
A two stroke would be measured the same as a standard engine. Our dip stick for stroke, and the spread finger tool for the bore. Of course the piston would have to be either high enough or low enough in the bore so that the fingers would not fall into the ports. Been done before. The standard math would be used to determine the displacement.
DW