When I fitted the K1100 TB's to my K100 there obviously wasn't one of these vacuum switches fitted. As the switch that was already fitted to my original TB's was so badly corroded I simply taped the electrical connections up and out of the way and didn't refit it.

I recently acquired an original set of K100 33mm TB's and which had a brand new Vacuum switch attached. Out of curiosity I fitted it onto my bike. It immediately lowered the tick-over by about 50rpms and it might be my imagination but throttle response below 3000RPM seems a little more sluggish. I know it was removed from later models. What was its intended purpose??

Cheers

Fent

probably just some pollution control bs

they were frantic to tick all the right boxes to get tuv approval and global acceptance

It was supposed to force the ignition system to switch to a different advance curve at tickover. It didn't work and BMW junked it pretty quickly.

Thanks for input Charlie and Dai. Other than the slight drop in tickover revs, the effect if there is any is negligible. I'll keep it connected and see if there is any advantage to fuel economy.

Fent

Can someone post a pic or an image of the part and its location? The TPS?

There you go the unit on the right with the red vacuum tube attached.