Compression test is just sticking a gauge in plug and kicking over good with throttle WOT till gauge no longer rises, done with and w/o some oil shot in for sense of ring blow by.
Compression test short video.http://www.youtube.com/watch?v=ovvXnd7A ... re=related
Leak down is trickier and a bit dangerous putting 100 PSI on piston, as will spin crank connected to rear tire so w/o nailing brake down and/or wood stick shoved in spokes in 4th gear, might leap right past you and take a finger with it.
Here's a video on air cooled push rod and DIY gauge regulator. New costs over $100 but might ebay one or rent one or wait on me to send ya mine. Air compressor required. http://www.youtube.com/watch?v=GvG22YMOzUI
Open up rockers and see if all valves move as expected. If none move, not likely but would imply cam not turning. Valves not seating, make sure the last in set enough. Combat 2S is .008" intake and .100" exht.
Not likely but possible head gasket blew out towards the push rod tunnels.
Air would leak into sump same as ring but more so.
Breathers vary -but all factory ones vent to oil tank then that vents to outside
or yuk into air box.