The goal of synchronizing the carbs is to
make sure both sides of the engine are performing the
same. This adjustment has to be made at 2 places -
idling, and throttle partially open, because 2 different
mechanisms control the openings.
First you will need some kind of device to measure
how hard the carburetors are working. Most use a device
attached to the vacuum nipple and measure the vacuum
side. You can also get devices that fit over the carb
mouth and actually measure the air flowing through them.
Since Ural carbs since 98 1/2 have the vacuum nipples
installed this is definitely the easiest way.
There are many gadgets for measuring the vacuum.
Fancy isn't required - you don't need an absolute
measurement; you just need to be able to compare the
left and right sides. If you review this board you will
find home made setups, mercury sticks, rotary gauges,
and electronic ones. All will do a great job.
Now, how to use them to balance your carbs!
Have the engine at operating temperature. It's a good
idea to have a box fan nearby to blow on the engine your
first time as it will take longer and you don't want to
overheat things. After you have some experience you can
do it quickly enough to skip the fan.
Attach your measuring device(s) and start the bike,
allow it to settle down to an idle. Look at the devices
and compare the cylinders. If you are using the vacuum
nipples, the higher reading means that side is working
LESS (it's further closed, (less gas), which makes more
vacuum). If you use a flow-measuring device the higher
reading is the one working harder.
If the bike is idling too slowly, pick the side with
the highest reading and tighten the phillips screw with
the spring on it that controls the idle. If it starts
idling too fast loosen the same screw on the other carb.
Tweak them until you have them equalized.
Blip the throttle a bit and let it settle down to
check your work. Readjust if needed.
This completes the idle portion of balancing the
carbs. Next you have to balance them at a partially open
When you open the throttle, the idle screws no longer
control the carburetors - the throttle cables do. If one
side is tighter than the other one, that side will work
You will need an 8mm wrench and a 10mm wrench to
adjust the cables.
Open the throttle some with the engine running and
compare the sides - just go easy, enough to clear the
idle screws but you don't want to wind the engine way up
with no load - aim for about 2000 rpm or so for a bit.
Note the levels and release the throttle.
In order to keep slack in the throttle I tend to pick
the one with the lower reading (with vacuum) and loosen
the cable on that carb by slightly unlocking the lock
nut and then screwing the ferrule down (clockwise). You
can do the other one, the main thing is to pick 1 carb
and stay with it for all your adjustments.
You'll have to use a little trial and error to find
out how much to turn the ferrule; try a small adjustment
at first and resnug the locknut or you'll get a change
caused by the looseness of the ferrule. Open the
throttle again and recheck. Repeat this until they are
as close as you can get them (you may not get 100%
equal, differences in cable drag, valve gap, etc can
cause some variations).
Essentially you are done; it's not a bad idea to swap
the measurement devices from cylinder to cylinder just
as a double check; some devices may not always read the
Shut the bike off, put the plugs back on the vacuum
taps, clean up and ride!