If you use after run oil, that is also where you have to put it in at. On a 4 stroke, it does little if any good to put the after run oil into the carb or exhaust port. If you use it, just a drop or two won't do, you need to put in about a teaspoon full and then manually rotate the engine to let gravity get the oil into the bearings on the crankshaft and connecting rod bearings. And yes, a lot of oil will come out of that vent in flight, probably about an ounce for every ten ounces of fuel burnt.