It's a check after a manual setting of the -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 manometer (e.g. Morgan Carbtune) or vacuum gauges, 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.)
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).