Adjusting the TPS (Throttle Position Sensor) on a 2V K bike

[frankenduck]

On a 2V K bike, it's actually just a switch, not a variable sensor.

The position of the TPS can be adjusted by loosening the two screws that hold it to the rear of the throttle body assembly.

It should be adjusted so that you can hear it click when any throttle is applied from a closed throttle position.  It's easiest to hear the click if the bike isn't running.

[Lawrence]

I'd like some clarification on this.  I moved the throttle position sensor on my 1985 K100RS before I knew what I was doing. Now the bike won't idle reliably.  The revs drop lower and lower until the engine stops. 
What function does this mechanism perform? Does it control fuel injection? Ignition advance?
The test routine is to listen for a click when the twist grip moves the throttle valves off their idle stop.  Must the ignition be on for this click to happen? I presently can't hear any click with the ignition on or off.   :dunno  The sensor is now positioned near the top of its adjustment range.
Based on the slotted ears of the unit's case, I suspect there is a cam on the end of the throttle arm (axel?) that, as it rotates,  contacts something in the throttle position sensor, correct?
TIA

[frankenduck]

It's actually just a switch, not a sensor, on the 2V bikes.   You should be able to hear it click whether the ignition is on or off.  Loosen it's hold-down screws and rotate it to each extreme with the throttle at idle.  You should be able to hear it click to find its sweet spot.

[rdilaure]

Hi.  I have been lurking here, getting lots of great info and this topic is one I have experienced.
My old ears, unfortunately, cannot hear that switch click (while installed on the bike).  I found that it is most accurate to set it with a
continuity tester or ohmmeter, as follows (ignition is off for this):
1.  Disconnect the plug from top of TPS.  There are 3 contacts in the switch which are now accessible.
2.  Clip leads of ohmmeter from middle contact (on switch, not cable) to 1st and middle contacts (counting from side closest to fuel injectors)
3.  With throttle fully closed, you should read 0 ohms.  When you rotate the throttle grip, the circuit should open (infinite resistance).
     Backfiring occurs when you never get the 0 ohm reading at closed throttle. 
4.  If you don't have a zero ohm reading at closed throttle, loosen the screws holding the TPS and rotate until the ohmmeter shows the circuit closure.
5.  Retighten screws and reattach cable.
6.  Go for a ride.

You can still get backfiring with this correctly set, if you don't completely rotate the throttle closed when coming to a stop.  That is because you are not allowing
the switch to close. However, this is controllable and doesn't happen often.

To use a test lamp (continuity tester) connect the first or middle contact of the switch to ground and connect lamp to battery positive.  Touch the probe to the
contact 1 or middle (whichever one you did not ground) and follow instructions from step 3.
I took the switch off the bike to measure it and found no continuity from 1 to middle when rotated fully closed.  So I got a new switch ($100 - Ouch).  I found
when playing with the new switch that it requires forcing it slightly at full closure to click the contact - and you CAN hear it.

Anyone need a switch?  I now own a spare

[WayneDW]

Thanks, Ron,

[frankenduck]

Or you could use one of these: