For all the insomniacs out there
I think the procedure is thus.
Procedure (reference BMW or Haynes manual for location of components):
1. Generously loosen the free play at the throttle cables to both left and
right throttle bodies (note '96 and newer "Oilheads" have a different
throttle cable mechanism--see manuals)
2. Unscrew the left throttle body throttle stop screw (under and inside of
the throttle body) counterclockwise (CCW) about three turns or until you can
see a gap between the end of the stop screw and the flange it pushes on to
open the throttle. You are now assured the left throttle is FULLY closed.
This is important! ("Zero" throttle opening).
3. Attach the Digital Voltmeter (DVM) black lead to frame ground and the red
lead to the red/white wire going to the TPS connector located on the left
cylinder throttle body. The TPS is a black plastic 2" by 2" square module
with a connector on the bottom. Gently pulling the rubber connector boot
down will expose the four wires entering the connector to the TPS. Probing
and pushing up with a paper clip is one method of reaching the red/white
wire's contacts. Put the DVM red lead on the paper clip, turn on the
ignition and engine cutoff switch, and retract the sidestand. You should see
an indication on the DVM near zero. Be SURE you are on the DC Volts
selection.
4. Loosen the two Allen head screws securing the TPS. Adjust the TPS by
slowly turning it within its slots until the observed voltage decreases to
about .006 DC volts. It will probably go no lower, which is OK. DO NOT turn
it any more as the wiper of the pot has already reached the end of
electrical travel. Stop turning the TPS just when the voltage stops
decreasing and then turn it in the opposite direction to increase the DVM by
.004. Lock it down there. Going slightly up by .004 volts will ensure your
are not going "below" zero volts and this will typically result in a "zero"
value of .010 volts. Be careful of DVMs which "autorange" and can confuse
readings! ("Zero" TPS voltage .006 +.004 volts = .010)
5. With "Zero = Zero" set (zero throttle plate opening and zero voltage),
turn the left throttle body stop screw clockwise (CW) until the voltage
starts to rise. Continue turning until you reach .370 - .400 volts, the
voltage the BMW analyzer looks for the TPS at idle to cause a digital signal
to "flop" or change symbology. Lock down the stop screw with the jam nut if
so equipped (early units are an interference fit). Blip the throttle several
times to check accuracy and repeatability of the voltage to be within .370 -
.400 volts. Readjust the stopscrew (not TPS Allen screws!) if needed.
Following this, reset the left throttle cable free play to .5mm. Now you are
forever done with the TPS adjustment.
6. Connect the mercury or electronic manometer to both throttle bodies.
Prior to starting the engine, use a common screwdriver to lightly close both
rear-facing brass air bypass screws on the throttle bodies, then open them
to:
R1100 RS/RT: 1 1/2 turns from closed
R1100 GS/R: 2 1/4 turns from closed
R850R: 2 1/4 turns from closed
Start and warm up the engine to get 5 bars on the RID oil temperature if so
equipped. Idle will be rough due to the need to synchronize left to right
throttle bodies. Use a big rear-facing fan from the front of the bike to
control cooling, if required.
7. After warm up, LEAVE THE LEFT STOP SCREW ALONE! (The one used to set
.370- .400 volts). Adjust the right throttle body stop screw to get
perfectly equal mercury in both columns or electronic indication.
8. Adjust the right throttle body cable for equal mercury readings at just
off idle, around 1500 RPM. Use the throttle to increase RPM, not the "choke"
start lever when synching.
9. Finally, adjust both brass bypass screws individually or together in
conjunction with the manometer to yield a proper idle speed of 1000-1100 rpm
and equal mercury or vacuum readings. Closing the bypass screws will
decrease RPM; converse for opening them. On rare occasions where proper idle
speed cannot be set with the bypass screws, return to step 5 and
incrementally increase or decrease the stop screw voltage from the .370 -
.400 setting then repeat subsequent steps. Raising the stop screw voltage
will increase idle RPM and decreasing it will lower idle RPM.
10. Inspect your work and test ride, perhaps re-performing synch using ONLY
the bypass screws and right throttle cable to "fine tune."
Summary:
The TPS was set for zero volts at zero throttle plate opening (+.004 volts
to assure not going "low"). Then the left throttle body TPS was set using
the stop screw to .370 - .400 volts followed by an accurate synch of the
right throttle body.
Results:
This is a simple procedure and it has worked on countless "Oilhead" BMWs.
You will notice good throttle response, best possible fuel consumption,
little if any surging and good top end. Properly performed, emissions are
unaffected if not improved.
(now moved on to the more technially advanced elastic bands method)
Should have kept me big gob shut
