Kuryakyn 9930 Bluegrass Breather Kit Unfortunately, almost all Harley-Davidson&#174; engines that vent the crankcase through the cylinder heads also expel oil through the same passages. Venting directly into the air cleaner, especially a free-flowing air cleaner, often results in an oily mess on the side of the bike. The banjo fittings and chrome tubes route the vented gasses upward so gravity can keep any expelled oil droplets in the engine where they belong. It is recommended venting the crankcase to open air by running the vent line up and out of sight beneath the tank, but an optional catch tank is available (and sold separately) for those who would rather vent to a closed container. Notes: Fits 1993 - 1999 EVO Big Twin with Mikuni HSR series carburetor, 1991 - 2013 Sportster models with carburetor or EFI.