Mid-range
surging is a common affliction among owners of R1100-series
motorcycles. Typically occurring between 2500 and 4500 rpm.
(it varies from bike to bike) and most noticeable in low gears
when the engine is not pulling hard, surging manifests itself
as continuously changing engine speed under constant throttle.
It is exceedingly annoying, but, thankfully, many R1100RT
owners report that their motorcycles' surging has gone away
as the engine began to break in. If you have a low-mileage
RT that is surging, it may be worthwhile to be patient and
work closely with your mechanic rather than attempting the
remedies described below.
Not
all R1100-series BMWs exhibit surging; it is apparently
more common among U.S.-specification motorcycles than among
R1100-series motorcycles sold in other markets. Surging
is commonly attributed to the extremely lean fuel mixture
utilized in the U.S.-spec R1100 engines and can be more
noticeable in oilheads that have not been carefully adjusted
by a competent mechanic.
BMW's
first attempt at a "fix" for the surging problem
was a lower-friction throttle cable. Throttle body synchronization
is key to a smooth-running oilhead motor and early R1100-series
models had "sticky" throttle cable that made throttle
body synchronization difficult. BMW warranty service bulletin
#2748 dated 7/3/96 outlines the procedures for replacement
of the cable for R1100 RTs with a VIN under 0440499. Most,
if not all, affected motorcycles are likely no longer under
warranty, but, if you own an early RT, it is worth checking
to see if the cable has been replaced. Furthermore, since
the cables do stretch and wear with use, BMW recommends
that your throttle cable assembly be replaced every 24,000
miles.
A variety
of other "fixes" have been reported, including
(1) replacement of spark plugs, (2)
throttle body synchronization, (3)
"zero = zero" adjustment
of the throttle position sensor, and (4) replacement
or removal of the cat code plug and other components.
WARNING:
While
owners have reported many instances in which these modifications
or adjustments have cured their motorcycle's surging,
you should be aware that these modifications - particularly
if attempted by a someone other than a competent BMW
mechanic-may decrease performance or cause damage to
your motorcycle. If BMW determines that there is a causal
relationship between any non-BMW-approved modification
and subsequent damage, any warranty claim will almost
certainly be denied.
A number
of R1100 RT owners have reported that simply changing to
different spark plugs has eliminated or drastically reduced
their machines' surging. Among those plugs which have been
reported to reduce surging are the following:
Bosch
is the OEM Supplier and makes several types of plugs:
Bosch FR5DTC (3-electrode)
Bosch FR6DDC (2-electrode)
Bosch 4418 (4-electrode)
Non-OEM:
Autolite 3923 (1-electrode)
Champion RC9YC or RC9YC4 (1-electrode)
NGK 4563 (3-electrode) (old #BCP6ET)
The
NGK 4563 plug, which is reported by Dan Abbott to have significantly
improved his RT's performance, is a non-resistor type plug,
which will likely cause interference with other electronic
gizmos-such as stereos-that are powered off of your RT's
electrical system. Some RT owners have expressed concern
that the use of non-resistor plugs could damage the Motronic
system, though, at this point, no instances of actual damage
have been attributed to non-resistor plugs by contributors
to this BBS. Dan indicates that the resistor-type equivalent
is the NGK 2164. As of this writing, no RT owners have reported
using the NGK 2164.
A very
important caution: You should be very cautious in substituting
plugs of a longer length than the OEM Bosch plugs. While
all of the plugs described here as possible substitutes
have reportedly been used by oilhead owners with good results,
the installation of an overly long plug could result in
it contacting a piston, with disastrous mechanical consequences.
Improper
throttle body synchronization is reportedly the cause of
surging in many oilheads. A competent BMW mechanic should
be able to accurately synch your motorcycle's throttle bodies,
but, unfortunately, a number of owners report poor results
when they have turned to their dealer's mechanic for this
adjustment. For those with the equipment and the willpower
to give it a shot on their own, Stephen Karlan has posted
an article on throttle body synchronization procedures on
the IBMWR web site. His article can be found at: http://www.ibmwr.org/tech/r11tech/r1100_throt_bod_sync.html
(incidentally, the IBMWR web site has a number of excellent
articles on mechanical issues).
Sean
Franklin writes "Some consider Rob Lentini's "Zero
= Zero" advice gospel on the subject of correcting
surging." Rob Lentini, an officer of the BMW
MOA and a well-regarded mechanic, has devised a non-factory-approved,
method of adjusting the TPS which can help in smoothing
a surging oilhead. It can be found at:
http://www.ibmwr.org/tech/r11tech/zero.html.
Lentini
cautions that this procedure should be attempted only by
"a reasonably skilled mechanic with knowledge of Motronic
fuel injection theory of operation." If you meet those
criteria and possess a digital voltmeter and a mercury or
electronic manometer, this procedure can result in a reduction
or elimination of surging. However, it is worth noting that
even Lentini cautions that it is worth simply trying to
swap spark plugs (he recommends Autolite 3923s) before attempting
this more drastic procedure.
Tomb9
utilizes a different procedure: "I've spent some time
diagnosing my surging, and I have a slightly different take
than the zero-zero adjustment. As mentioned in other posts,
the surging is a result of the overly lean mixture on US
bikes. The zero-zero procedure attempts to adjust the TPS
to richen the mixture, but misses the point. The fuel injection
uses the TPS to indicate throttle opening, so it can be
adjusted to increase the amount of fuel without increasing
the amount of air. The results are a richer mixture. The
procedure is simple. Pull your left fairing cover. Get out
your trusty DVM and attach the minus side to the battery
negative terminal. Attach the plus side to a pin and stuff
the pin into the end wire of the TPS connector (red/white).
Turn on the ignition, but don't start the bike. The DVM
will now read between .300 and .400 volts. The optimum setting
is .395. Loosen the screws that hold the TPS in place, and
rotate the TPS until you get 0.395 volts. Tighten the screws
and crank on the throttle a few times. Reset the screws
if required to get the correct voltage."
Engine
control and emissions components used by BMW vary significantly
from country to country. U.S.-market R1100 RTs employ components
to conform with (and, in fact, exceed) the stringent emissions-control
requirements of the U.S.A. Some owners report that removal
of the cat code plug, combined with the installation and
proper adjustment of a potentiometer, reduces or eliminates
surging.
TomK
reported: "I had my dealer change the fuel and exhaust
system to Canadian specs. For a cost of about $200 the change
was dramatic." TomK indicates that the BMW part #s
for the required modifications are:
- 13621461425
CO Potentiometer
- 13621341499
CO Potentiometer carrier
- 13541460594
Vacuum nipple cap
According
to FrankT, the procedure was outlined in "the July
issue of Rider in the Tech Q&A column on page 89. It
indicates using a foreign market cat code plug and the potentiometer.
The article indicates that the potentiometer gets adjusted
with the use of an exhaust gas analyzer to 2.5 percent CO
at idle, or if no gas analyzer is available, pretend you
are adjusting a carburetor for the best lean idle and smoothness."
Again,
Rob Lentini has experimented with several variations on
this theme, including substituting the Swiss-market cat
code plug. The results of his experiments can be seen at:
http://www.ibmwr.org/tech/r11tech/R11inj-surging-fixes.html
Of course,
the usual caveats regarding the possible impact on your
BMW's warranty apply. One additional caution is in order:
some of these modifications will damage your catalytic converter.
If you ever decide to restore your motorcycle to its stock
configuration, replacing the cat is a big-dollar item. Moreover,
Shotgun1897 reports: "If you use an exhaust with a
[catalytic converter], you can not adjust the mixture using
an exhaust gas analyzer with the CO potent & the cat
will clog and will cause back pressure and heat build up.
If this happens it will take out the exhaust valves."
Surging
is a tremendous annoyance, but if you are riding a low-mileage
RT there is an excellent chance that the surging will disappear
as the miles add up. If your motorcycle is still under warranty
and the surging is unacceptable, your first step should
be to take your motorcycle to your BMW dealer; surging can
often be rectified by a competent mechanic using factory-approved
procedures. Be persistent with your service advisor and
dont take any excuses for a bike that runs poorly.
If all
else fails, or if you simply want to try to further improve
your RT's smoothness and power, the procedures outlined
above may be the way to go. When attempting these modifications,
stay within the limits of your mechanical ability; some
of these modifications, if done improperly, will damage
your motorcycle. Bear in mind that any damage caused by
your modifications may negate your warranty.
