K Bike Tech

K Bike Mystery Hose

The first time you look at your K bike motor from the right side you may see a "mystery hose" that is usually capped off with a check valve, screw or something else. The hose looks like it goes somewhere to the front top middle of the engine. It does. It goes to this vent pipe:

Does it matter?

No.

Why is it there?

There's a pipe under the right rear of the gas tank for venting gas fumes. In order to meet California emissions standards K bikes needed to vent these fumes back to the engine. From the factory there was a hose between the tank's fume outlet pipe to the pipe at the front of the engine. (Which is a PITA to reattach when you take the tank off and then reinstall the tank.)

What's the rear tank pipe for?

With the gas cap open you will see a notch in the left side of the perimeter.

This is where water drains from around the gas cap when it's raining. It drains to the rear pipe.

"The Cup"

In order to make dealing with tank removal/installation easier, at some point in time BMW produced a rectangular "cup" to sit below the tank outlet pipes. More info about "the cup" can be found at this link.

Alternative To The Mystery Hose

If you ever have the radiator off then you can get rid of the mystery hose and just put a rubber cap on the pipe at the front of the engine.