As piston travels down on powerstroke, intake charge is compressed in crankcase and forced into combustion chamber when transfer ports are opened up. As piston travels up on compression, it also creates a vacum in crankcase sucking in fresh fuel/air charge. With a blown gasket it will also suck straight air without fuel/oil mix into crankcase,causing EXTREME lean condition, causing sputtering, causing melted piston, dry bearings, causing catastrofic engine failure. PLEASE do not run it until you fix the gasket. A complete top end gasket set will cost you about $20, 2 base, 2 reed, 1 head gasket. A CLYMERS manual is $25-$30. Someone on here has a video/ moving drawing of a two stroke in his signiture, shows what goes on with a two stroke with a chamber. It will also force air /fuel/oil mix out of blown gasket .