By Rob Lentini <roblentini@cox.net>
'87 K75S
Tucson, AZ
K Whiner MC#11


First of all, are you having problems with your bike? The only reason that you should really have to go into the air flow meter is to correct for relaxation of the return-to-zero spring inside. With age, its preload weakens resulting in a richer mixture that can manifest itself by black sooty smoke from the exhaust.

To determine the meter's condition, you will need access to an exhaust gas analyzer. If you don't have one, maybe your dealer will do the check for you.

Anyway, with the bike thoroughly warmed up, and a large fan blowing at the radiator, measure CO at idle and at the first and second detent of the "choke" lever. You're looking for about 2-2.35% at idle, and 1-1.5% at the higher speeds. Really lean mixtures may cause backfiring on trailing throttle. Be advised that a too-rich mixture at idle will affect, to some extent, higher rpm readings, so set the air bypass adjustment screw on the top of the air box (under the rubber cap) for 2-2.35% first.

If cruise CO is too rich, remove the top section of the air box from the motorcycle. Now carefully remove the meter from the airbox (careful with the connector!) and carefully, VERY carefully pry off the black plastic cover over the potentiometer assembly. Now install the meter to the injector plenum by removing the snorkel from the airbox and connecting it directly to the meter and then to the plenum. This will enable you to run the bike and adjust the mixture in real time.

Look at the potentiometer assembly. You will notice a toothed adjuster wheel that controls spring tension. It is held in place by a metal clip. You should be able to gently raise the end of the clip off the teeth to turn the wheel. Turning the wheel CW from the top will lean the mixture, and vice versa.

Running the engine with the open potentiometer and at the fastest position of the "choke", change the wheel to achieve 1-1.5% CO. Only move the wheel one tooth at a time, and remember WHERE you started from!

Once satisfied with the CO reading, and seeing no sooty smoke when you blip the throttle, you are done. Remove the meter and delicately clean the carbon resisitive element that the wiper runs on with a Q-tip and alcohol. Make sure there is no crap inside the chamber by gently blowing it clean with a camera blower/brush. Reseal the cover to the meter using BMW Drei Bond silicone ONLY. Other types will leave acid fumes inside, possibly corroding delicate parts. Let the meter cure overnight and reinstall. You may need to reset the idle CO more lean after installation, due to whatever slight airbox restriction exists.

So, that's it! You will be rewarded by better throttle response, fuel economy, lower emissions, and maybe even better power. Just use EXTREME care when doing all this. The meter costs about $800!!!

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