The fuel injection control unit (a.k.a L-Jetronic) is an analog "computer" and unlike many later units does not sense and adjust the mixture for the lower air pressure found at higher altitudes. On US models of 2V K bikes, BMW incorporated something commonly referred to as the altitude plug. When passing through an altitude of 4,000 feet you either insert (above 4,000') or remove (below 4000') the altitude plug.
The connector for the altitude plug can be found along the frame rail above the back of the throttle bodies. The picture below shows the connector with the factory black protective cap installed. Sometimes it's hidden behind the frame so you have to dig to find it.
The altitude plug is BMW part # 61 13 1 459 504. All it is is a loop of wire that shorts two leads.
If you travel through an elevation of 4,000' when touring or riding in the mountains then it seems kind of silly to have to stop and remove or insert the altitude plug. If you've got an extra switch slot in your handlebar dash pad then it's very easy to add a switch to take the place of the altitude plug. All you need to do is cut the wire loop of the altitude plug and hook the wires up to a hazard switch. Part # 61311459305. (Or alternately cut off the receptacle for the altitude plug and wire the switch up directly.)
Then, when you pass through 4,000' on your way up activate the switch and turn it off on your way back down. :2thumbup:
