BMW R850 Maintenance Manual page 57

There is one black tube attached to the under side of each throttle body. Remove both
black (vapor recovery) tubes and you will expose the brass nipples that point down.
Attach one of the carb stix's flexible plastic tubes to each brass nipple. Make certain that
the carb stix's plastic tubing does not touch hot exhaust parts; the tubing will melt. There
is no need to plug the black vapor recovery tubes.
Starting the Adjustment:
Loosen the right side crossover synch cable by loosening the 10mm lock nut and turning
the knurled knob counter clockwise to ensure that there is slack ['97- loosen right throttle
cable] .
Count the turns you make to lightly seat both the right and left large brass bypass
screws by turning them clockwise with a flat screwdriver. Record this information for
possible trouble shooting later.
As a starting point, back out both large brass bypass screws 1 1/2 turns for an RS or
RT; 2 turns for an R or GS.
Start the engine. The bike may idle rough because it is not in synch. Do not be
concerned about a rough idle at this time. If the bike will not idle at all due to air
starvation, back both large brass bypass screws out by 1/4 turn (ccw) until the bike
maintains a rough idle.
If the bike is idling too fast, reduce the air flow by screwing both large brass bypass
screws clockwise (cw) in increments of 1/4 turn. If the bike is idling too slowly, increase
the air flow by screwing both large brass bypass screws counter clockwise (ccw) in
increments of 1/4 turn. At some point you will not be able to decrease or increase the
idle speed by moving the large brass bypass screws. Return to the setting immediately
prior to the point where the idle was not changed by moving the large brass bypass
screws.
You now have the large brass bypass screws at the starting point for the low rpm synch.
LOW RPM SYNCH:
With the throttle at idle (1,000 to 1,200 rpm on the tachometer) and the bike at normal
operating temperature, turn the right large brass bypass screw clockwise until the
mercury columns in the carb stix are at an equal height. If moving the right large brass
bypass screw does not accomplish equal height mercury columns, then reset the right
LBBS to its starting point and turn the left LBBS clockwise until the mercury columns in
the carb stix are at an equal height. The amount the mercury column rises or falls, its
actual height, is not important. What is important is that both left and right mercury
columns are the same (equal) height.
The goal is to balance the throttle bodies with the large brass bypass screws open as
little as possible (minimum counter clockwise opening). Bob Gorman notes that, when
adjusted correctly, the screws should be within 1/2 turn of each other.
If the bike does not adjust by turning the LBBS clockwise (in), or if the idle speed is too
low (below 1,000 rpm), change the starting point of the low rpm synch by backing out
both LBBS (counter clockwise) by an additional 1/4 turn.
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