BMW R850 Maintenance Manual page 58

HIGH RPM SYNCH:
When performing the high rpm synch, you will be moving the throttle up to
4,000 rpm. Move the throttle slowly to avoid sucking mercury into the engine.
The right side crossover synch cable has already been loosened ['97- right throttle cable
has already been loosened]. The knurled knob should turn without turning or binding the
crossover synch cable.
Adjust the knurled knob so that the mercury columns rise together as the rpm
rises. You may need several turns to take up the slack you created earlier. Some riders
adjust the mercury column heights with the rpm steady at 2,500, some with the rpm
steady at 4,000, and some make this adjustment so that the columns are fairly equal
while the throttle is being opened from 2,000 to about 4,000 rpm. The mercury columns
should be fairly equal if the throttle is held steady or while the throttle is increasing rpm
from 2,000 to 4,000.
After adjusting the knurled knob so that the mercury columns are equal, tighten the
10mm lock nut and recheck the mercury levels. If tightening the lock nut moves the
knurled knob and upsets the adjustment, hold the knurled knob with small pliers or
needle nosed pliers to maintain the adjustment. If holding the knob does not work,
measure the amount of mercury column error after tightening the lock nut. Recording
this measured error, loosen the lock nut and add the amount of measured error to the
mercury column before tightening the 10mm lock nut. This objective is to have equal
mercury column heights after the lock nut is tightened.
Test your work by checking the mercury level at idle and at 2,500 rpm. If not equal, you
should begin again with the adjustment process at "Low RPM
Synch".
Trouble shooting:
If the valves are not properly adjusted and are not equal side-to-side, the cylinders will
not be getting an equal amount of air-fuel and the throttle bodies cannot be
balanced.
Check that the air supply tube-throttle body connection is aligned, that the air supply
tubes are fully seated at both ends and that the clamps are correctly aligned
when tightened.
If, after satisfactorily completing the synch, the bike begins to vibrate wildly, check to see
if a small stone or other debris has become lodged in the throttle cable pulley.
This is a common problem.
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Where to buy carb stix, mercury:
Precision Manufacturing Services at 800-237-5947 was selling the Motion Pro brand for
$36.95 + shipping in 1996.
J.C. Whitney has a Motorcycle Accessories and Parts Catalog for $1. They show several
types of vacuum gages and mercury manometers. Their address is P.O. Box 3000,
LaSalle, Illinois 61301, phone 312-431-6102; fax 312-431-5625.
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