Steve: The filler cap in question is the
oil filler cap. I should not be vented to the atmoshere but only by hose to the air filter base. Some had gauze in them and were not attached to the air filter, the "closed system" consists or recyling the vapors from the crankcase breather/
oil filler tube back through the air filter assy by a hose and requires a closed (non vented) breather cap.
Rick