Fuel Caps

Removing/replacing/rekeying other locks in the later Airhead (and Classic K bike), luggage, etc., will be found in Snowbum’s article 75A on his website, http://bmwmotorcycletech.info.

WARNING! ….BMW SCREW CAPS SHOULD NOT BE OPERATED LIKE AUTOMOTIVE CAPS!  AVOID spinning these motorcycle fuel caps to the ratcheting point when tightening them! The ratcheting parts WILL eventually wear out, and WILL eventually cause you problems in trying to remove the cap.   BMW Airhead fuel caps are not constructed like car caps. On most modern car fuel caps, the cap is designed to be rotated to the ratcheting point. That is done because the car caps must fully seal a complicated fuel fumes venting system; if a car cap is not rotated enough, the cap can leak fumes, which will likely be detected by the car’s computer monitoring system, and a “Check Engine” light will illuminate on the car’s dashboard. On our Airhead BMW’s, the cap for the earliest Airheads is simply designed to keep liquid fuel from sloshing out. Later models had cap vents and even later ones had simple venting to direct fumes to the crankcase. These last versions had a more complicated fuel cap, called a SHED cap, but it is best not to rotate them to the ratcheting position; even though that is often done by those locking their caps. If you do tighten to the ratcheting point, try to ratchet only one notch.  Much more on these various caps with the ratcheting mechanisms further down this article!

Fuel caps and venting methods for the BMW fuel tanks vary by year & model. For information on the Pulse-Air system, the fuel tank venting system, & other associated items, please read: http://bmwmotorcycletech.info/pulseair.htm

It is common to hear about an Airhead “running out of fuel”….stumbling, loses power, etc. The problem will often be the tank vent …or the fuel cap. Both problems can be identified by loosening the fuel cap and usually hearing a whoosh of air entering.  Within 15 seconds, the engine will then run OK. Engine stumbling from this venting problem usually happens much more quickly with a more-filled tank and also from high speeds.  While this fuel delivery problem can occur on the models with the fuel solenoid mounted on the underside of the starter motor cover, that is less likely.

There can be other types of problems, such as fuel leaks at the caps, etc.

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