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This area is a basic explanation of how you sync a multi-carb set on a Japanese Motorcycle.

Carb Synchronization

carb Synk vaccuum Gauge Set

On most multi cylinder 4 stroke bikes the carbs will eventually get “out of sync”.
The reasons for carbs to do this can vary but the results are the same. Less power, bogging
at various rpms, and poor performance. Most obvious sign is the lack of a steady idle point.
Your motor will rev high at times and want to die at other times. This is due to your carbs
fighting one another.

We hope this tip on how to sync your own carbs helps. Keep in mind bad jetting or a
damaged or “open” exhaust and electrical problems can cause these problems too. You
should get professional advise on weather or not a carb sync will work for you. I have
found a major difference in bikes I have synced.

First you must acquire a gasoline test tank. This is a tank that can feed gas to your
carbs while your tank is off the bike. (note: a antifreeze overflow tank from a water cooled
bike or car works nice. Most junk yards and bike shops have these on hand). Also motion
pro makes one for 40-50.00 that has a petcock and fuel line.

Next you must acquire a set of synchronizing gauges or sticks. The type I recommend
are the mercury filled type. They can be purchased for about 40.00.

Now, there are two basic types of carbs. The two types are standard and CV (constant velocity).
Standard carbs will have a small cap on the top that must be removed for you to sync them. The
CV carb ,usually on most all twins and most 4 cylinder bikes after ‘79, are easier to sync due to
 the fact that the adjustments are external.

The concept of syncing the carbs is to make the carb work at its most efficient level with the vacuum
available to it. One off sync carb can drag down the rest of the cylinders on power. So what you are
going to do is hook up a device (the carb synchronizer) to each of your carbs vacuum tubes and adjust
the carbs until they are all working on the same vacuum level.


So here are the steps.

  • 1 - Take off the tank to expose the carbs.
  • 2 - Hook up test tank. DO NOT FILL YET.
  • 3 - Find the carb or manifold vacuum hook ups. These are different from bike to bike. Some are on the
    intake boot (on the head) and are actually tubes with vacuum caps that you can remove. Others are a
    Phillips screw that can be removed from the head or front of carb to install the tubes that come with most
    sync gauges. And still others have the vacuum hook ups on the top of the carb. Most manuals will show this location.
  • 4 - Hook up your synchronizer to the bike by installing one hose per cylinder and set the gauges on a stable
    surface or hung safely.
  • 5 - If you have a older bike with standard carbs remove the small caps at the top of each carb.
     (if the cap is larger than 2” x 2” you may have CV carbs and this is not necessary). This will expose the carb throat adjustment.
  • 5b - If you have CV carbs, look between each of the carbs for a screw with a spring under it. These are the
    butterfly adjustments. Most 4 cylinder bike have only 3. One of the middle carbs is non adjustable. This is
    the carb used as a gauge for the rest of your carbs. You will be adjusting the other carbs to match this carb in
    vacuum level. Also make sure you have the proper tools to get to all the adjustments.
  • 6 - Next you need to find the screws to adjust the mixture. They are also on various locations and are sometimes
    covered with a aluminum plug to hide them. Make sure you have the tools to move the screw for the mixture.
  • 7 - Fill the test tank with good fuel.
  • 8- Start the bike (DO NOT REV UP). You may even want to warm the bike up before you start if you feel revving
    is necessary. You will need to set the idle at appr 1/4 to 1/3 of the rpm needed to reach the maximum torque level.
    Examples
    • KZ900/1000 max rpm for torque 8500rpm appr 2000-2500rpm
    • FZR1000 ‘87 max rpm for torque 10500rpm appr 3500 rpm
    • CB750K ‘75 max rpm for torque 7500rpm appr 2000 rpm
    • this may not be consistent with some directions for this procedure. I base this on personal experience only
  • 9- While the bike is running at the appropriate rpm adjust all the carbs to match the one of the center carbs
    that is not adjustable like the others.
  • 10- After step 9 bring the rpm back down to idle.
  • 11- Adjust all the mixture screws to their highest idle. This will be a very small difference in rpm but if you listen
     hard you will hear it.
  • 12- Now re-adjust the main idle to the normal level for your bike.

Now you should have a synchronized set of carbs that will make your bike more powerful and smoother than before.
If you have any questions about this procedure or where to find the adjusters on your bike Feel free to call or e-mail me.
SAFE HAPPY RIDING


Additional Information

Here is a link to a site about how to make the tool for YICS Yamaha's.

http://home.westman.wave.ca/~jbe/YICS.htm  (non functional link to save confusion.
You will need to cut and past to your browser to use) (You will want to use the link below
to see the instructions in such a way that allows return to our site) This is NOT our material.
It was copied from the link above. The actual tool is no longer available from Yamaha.
This link could save you time and $ The link was supplied by a customer that wanted to help.


LINK TO MAKING YICS TOOL