By Rob Lentini <>
'87 K75S
Tucson, AZ
K Whiner MC#11

Here's a manual method of setting L-Jetronic K bike fuel injection CO (carbon monoxide) mixture without the need for an exhuast gas analyzer:
  1. Thoroughly warm the engine.
  2. Remove the rubber plug from the top right corner of the air box, above the engine. Using a 5mm allen, adjust the air flow meter idle air bypass screw under the plug for highest attainable idle speed. This should be about 1-2 turns out from the fully-seated position CW.
  3. Using a Carb Stix mercury manometer or vacuum gages, reset the butterfly bypass screws to resynchronize and establish an idle of 1050 rpm, or about one tach needle width above 1000 rpm.
  4. Now turn the idle air bypass screw CCW (from the top) until rpm is lowered by 50 rpm to 1000, about 4-5 total turns out. (This is called the lean drop method of setting CO, if you don't have an exhaust analyzer.)

If you live above 4000 ft elevation, be sure to install the high altitude compensating plug into the harness. There's a receptacle taped to the frame on the left under the side panel.

As a final check, you know you have done it all correctly when:

  1. You press the starter button with the engine running and the rpm stays the same or slightly increases (enriching signal to the computer).

  2. You pull out the high altitude plug and the rpm also increases (again, enrichening signal to the computer, but less so than the starter. You've set it lean, so enrichening will increase rpm).

Don't forget to reinstall the rubber plug. I've also assumed you've got a 2 valve K with L-Jetronic injection. Motronic works differently. Have fun!


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