Throttle Body Synch - Stephen Karlan - BMW R850 Maintenance Manual

Throttle Body Synch – Stephen Karlan (Dali Meeow)
An out-of-synch condition develops (R850 and R1100) because the throttle body cables
stretch or because they lose their adjustment. The result is vibration, sometimes unreal
vibration.
The following procedure, which I call the Gorman/Diaz Balance, was developed by Bob
Gorman and Jon Diaz from Chicago. It is a fast and simple procedure that can yield
dramatic riding improvement.
The 1994-96 models have a crossover synch cable; the 1997 model has left and right
throttle cables attached in an upside down "Y" pattern. Use these instructions for the
1994-96 models. If you have a 1997 model, look for the ['97 - ] and follow the
instruction inside the brackets and disregard the instruction given immediately prior to
the ['97 - ] brackets.
Overview:
The throttle bodies will be synched at two rpm levels.
The low rpm synch will be done first. With the bike at idle (1,000 to 1,200 rpm), the large
brass bypass screws will be adjusted. (LBBS in the Glossary at the end of this article
will help you find this part.)
The high rpm synch will be done last. With the bike at 2,500 to 4,000 rpm, the right side
crossover synch cable will be adjusted. (RSCSC in the Glossary at the end of this
article will help you find this part.) ['97 - right side throttle cable will be adjusted.]
Tools needed:
mercury manometer (carb stix) and a way to secure it (several places to obtain the carb
stix are given at the end of this article)
small pliers or needle nose pliers
10 mm wrench
flat screwdriver
pencil and paper.
Setting Up:
Remove the right side black plastic fuel injection plug cover for access to the right side
crossover synch cable ['97- remove cover for access to right throttle cable]. If you have a
lower fairing, remove it to allow air to reach the cylinders and to prevent cooking the
fairing. With the bike on the center stand, retract the side stand, put the transmission in
neutral, turn on the bike and warm up the engine. Jon Diaz
suggests a more enjoyable way to warm up the engine -- take a ride.
Position a fan near the front tire with its output directed at the cylinders equally to avoid
overheating, or use two fans, one directed to each cylinder. If your bike has a Rider
Information Display (RID), allow the oil to heat up to 5 bars, otherwise idle the bike for
five minutes.
Secure the mercury manometers (carb stix) on the right side of the bike, where most of
the work will take place. Use any method that secures the carb stix (and the hazardous
mercury) vertically while the bike is running, such as hanging the carb stix from the
ceiling.
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