Air Accumulator (a.k.a. "The Cup")

Air Accumulator (a.k.a. "The Cup")

All K bike gas tanks have two vent pipes protruding from underneath the right middle rear of the tank.

Oftentimes these are connected to two hoses. The forward hose, from the factory, went to a vent on the top of the engine block above the middle of the timing cover. This was so that gas/fumes would vent back into the engine to meet California emissions requirements. The rear hose was an overflow hose that drained to the pavement behind/under the right side peg plate. Its source is the hole at the left side of the gas cap.

Many times the vent on the front of the engine has been capped and the hosed plugged since it really doesn't do much.

These hoses can be a pain to keep connected and also keep unkinked when re-installing the gas tank. An alternative is to install "The Cup" under those two vent pipes. (BMW part 16132307467 - Air Accumulator - about $5)

Attach a hose to the pipe at the base of the cup to drain behind/under the right side peg plate. You can reuse the old hose from the rear pipe for this. It already follows the correct path.

Here's what the part looks like:

To keep it in place, drill a hole in it and use a zip-tie to hold it to the frame:

The upside of doing this is that it makes tank removal and installation much easier and you don't have to worry about those vent hoses getting kinked. The downside of doing this is that you might occasionally smell a whiff of gas when riding. Big deal.