and coupled to all that.
its just a tin. the crankcase on a fourstroke is full of air and oil. when its running, that oil is turned to mist.
the piston going up and down turns the crankcase into a pump. air goes in, air goes out. on a multi cylinder, therell be a pcv with breather hose to air intake or catch can.
on a small engine its usually a hose from a "dry" place in the crankcase(rocker cover etc, only oil mist) to a connector on the carb/aircleaner.
robin subaru do use a pcv type valve on the lil engines. makes using different aircleaners tricky... its necessary and cant be removed! but they still have a breather
any oil that is blown through is simply ingested and burnt. that does tend to make plugs go black and smoke things up. ikky. the whole thing leaks and gets yukky.
so block off the hole on the carb. run the hose to a fairly large tin instead... make it a fair bit bigger than the cylinder capacity... alloy drink flask would do.
you have to do this if you change the aircleaner and or carb from stock anyway.
the tin wants some internal baffles,(lots of stainless scourer pads? drilled pipe? etc...) an easy way to drain it occasionally (or permanent return to engine sump) and its own breather hole.
you do not want to close the breather hose off if it was open in the first place.