Throttle Screw And Tps Adjustment - Stephen Karlan - BMW R850 Maintenance Manual

Throttle Screw and TPS Adjustment - Stephen Karlan (reviewed
by Rob Lentini)
I. The Problems.
Surging -- A condition of increasing and decreasing power, cycling back and forth, when
the throttle is held absolutely steady at a fixed rpm (such as 3,500 rpm while using a
throttle lock, tape or rock-solid hand). The electronic control system is hunting (up and
down) for the correct air/fuel mixture and the engine is not responding to throttle input
but to electronic sensors.
To minimize surging, the throttle plate screws (two) and the Throttle Position Sensor
(one TPS on the bike) are adjusted using a voltmeter. (There can be other factors, but
an incorrectly set TPS is the 95% problem.)
Vibration -- Shaking or oscillating. When the throttle is held in a fixed position, the
vibration is constant and unchanging. It may vibrate more at one throttle opening (rpm)
than at another; i.e. it may vibrate more at idle (or is more noticeable at idle) than at
3500 rpm.
To minimize vibration, the throttle bodies (one for each cylinder on each side of the bike)
are balanced using mercury columns.
Ensure that the valves have proper clearances before starting any fine tuning and that
plugs and wires are operating correctly. Instructions on performing a valve adjustment
can be found at http://www.ibmwr.org/rtech/r1100_valve_adjust.html
II. The Approach.
It is quite possible that a bike has both a surging (throttle plate screws and TPS) and a
vibration (throttle body) problem. With these instructions, you will address the surging
and vibration problems in that order. If you do not have a surging problem, DO NOT
adjust your TPS ! If you do not have a surging problem, DO NOT adjust your TPS ! If
you are not sure about your problem, then do not continue with these instructions and,
instead, balance the throttle bodies using "Throttle Body Balance for Dummies". In fact,
I strongly recommend that you balance the throttle bodies at least twice before you use
the instructions in this article. Throttle body balancing is relatively fast and easy to
accomplish and, you will need to balance the throttle bodies as part of setting the throttle
plate screws and TPS.
In addition to surge and vibration, some bikes will present an idle anomaly in which the
idle will be too high. The idle problem, which is nothing more than an idle in excess of
1200 rpm, occurs most frequently on GS and R models after resetting the throttle plate
screws and the TPS. This problem is addressed at the end of the TPS adjustment
instructions. Idle speed also is addressed in "Throttle Body Balance for Dummies" if you
are only performing a throttle body balance.
The basic knowledge about adjusting the TPS and basic throttle settings to obtain
optimal engine response is the work of Rob Lentini; his Zero=Zero article appeared in
MOA's Owners News and is on the IBMWR web site at http://www.ibmwr.org/tech.html.
This article does not present significant or new procedures, it has been written for
newbies and simply goes into greater detail. It was designed to help you find the right
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