Ok I remember now. When it fires, the exhaust ports are higher in the cylinder so spent gas is discharged, there first, then as the crankcase has been loaded on the firing stroke by vacuum, the downstroke forces that charge which is now trapped by the reeds, or in some cases a rotary valve, that creates pressure in the crankcase. Then as the top of the piston clears the intake ports, that pressurized fuel mixture is "forced" through the intake ports and then the piston returns on the compression stroke for a fire. Lets go back......then while the piston is heading back on the compression stroke, it creates a vacuum or suction into the crankcase. So yes, the suction part of the operation is what gets into the crankcase, the pressure side of the operation is what gets into the cylinder. Its a 2 step process. Withou one, we don't have the other..
So, if air can't get "sucked" into the crankcase as the piston is rising, then we have little hope of a good or accurate compression test. Right? The ports are not configured to get an air charge by way of the exhaust side, brother.
My old science teacher would be proud. I can make em run, but how the he## does it work?