at the lowest speed at which the engine will idle
4. Rev the engine a couple of times to see if it
settles down to the set speed. Readjust, if
Idle Mixture Adjustment
The idle fuel/air
emissions, as well as idling stability and
response off idle; see
Idle Mixture Adjustment
in Chapter Seven.
On motorcycles imported into the United
States, the idle
screw is set and sealed
at the factory and requires no adjustment.
Synchronizing the carburetors makes sure
that one cylinder doesn't try to run faster than
the others, cutting power and gas mileage. The
only accurate way t o synchronize the
carburetors is to use a set of vacuum gauges (a
manometer) that measures the intake vacuum
ofall cylinders at the same time. A typical set of
gauges is shown in Chapter One.
Before you try to synchronize the
carburetors, m a k e sure all of the
following are checked or adjustedfirst;
not, you won't get a good synch.
h. Spark plugs
c. Air suction valves ( U S . models)
d. Valve clearance
e. Point gap and ignition timing
J Throttle cable play
g. Carburetor holders and clamps air-tight
1. Ride the bike to warm it up fully, set the idle
speed, then stop the engine.
2. Remove the rubber caps or vacuum line
from the vacuum t a p in front of each
B, Figure 82) and attach a set of
vacuum gauges following the instrument
3. Turn the fuel tap to PRI (prime), start the
engine and check that the vacuum difference
between the cylinders is less than 0.80 in. Hg
(20 mm Hg). Identical readings are desirable.
4. If the difference is greater than specified.
remove the fuel tank; see
Fuel Tank Removal
in Chapter Seven. Hook up a temporary fuel
supply or use a long fuel line to connect the
carburetors to the fuel tank. Plug the vacuum
line that goes from the carburetor to the
vacuum fuel tap.
W'hen supplyrng fuel by temporary
means, makesure the tank
all fuel lrnes are trght-no leaks.
5. Remove the caps from the carburetors
(Figure 83) and loosen the synchronizing screw
locknuts (Figure 84).
is shown with the carburetors
removed for clarity. Do not remove the
carburetorsfor this procedure.
6. S t a r t t h e e n g i n e a n d turn each
synchronizing screw until all vacuum readings
are within specification. Hold the screws
steady while you tighten the locknuts.
7. Rev the engine once and check that all
cylinders return to equal readings. Readjust if
necessary and tighten the adjuster locknuts
while holding the adjusters steady.
8. Reset the idle speed, stop the engine and
install the carburetor caps and vacuum lines or
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