You could just vent the block outside, but the original carb (and many B&S carbs) draw the vented air into the carb for a fuel heater, and to facilitate the engine HP (operates in vaccum) I tilted the tiller pretty far today (almost fell over in a rut)while running, and it sucked some oil into the carb. It kept running but smoked for a couple minutes.
I used to use a similar hose plugged into the filter box of an old BS mower with foam element to replace paper. It would oil the filter for me in use. I suppose it lubricates the motor a little.
The hose carries a pulse that corresponds to engine RPM, and blows oily air from the crankcase. You can run this engine without this hose directing back to the carb/manifold, but you must secure it so it can breathe, and keep debris out of it. Oil may be blown from this line if the engine is tilted or leaned on an incline. Do not allow water or condensation to get into this or it will pollute the oil. If it is directed into the carburetor it adds a small amount of oil to lubricate the cylinder and it is burned off, instead of just venting to the air, and the vaccuum lets the governor work smoothly.
