Freebird Posted August 18, 2006 #1 Posted August 18, 2006 Synchronizing The Carburetors WARNING! Please be aware that the Yamaha Service Manual has the procedure for syncing the carburetors WRONG. The manual indicates that screw 1 is used to sync carb 1 to carb 2 and that screw 3 is used to sync carb 3 to carb 2. That is opposite of what it should be. The following is the correct procedure. NOTE: Prior to synchronizing the carburetors, the valve clearance and the engine idling speed should be properly adjusted and the ignition timing should be checked. 1. Stand the motorcycle on a level surface. NOTE: Place the motorcycle on a suitable stand. 2. Remove vacuum plugs. 3. Install: Adapters Vacuum gauge (Fig.2) Engine tachometer (Fig.2) to the spark plug lead of cyl. #1. Vacuum gauge: YU-08030-A, 90890-03094 (These are Yamaha part numbers. Any suitable mercury sticks, or other suitable gauges are just fine) Engine tachometer: YU-08036-A, 90890-03113 (Yamaha part numbers. Any suitable tachometer will work. A tachometer is not absolutely required 4. Start the engine and let it warm up for several minutes. 5. Check engine idling speed. If out of specification, adjust to 950 to 1050 RPM. Refer to "ADJUSTING THE ENGINE IDLING SPEED". in your service manual 6. Adjust carburetor synchronization. A. (Fig.3) Synchronize carburetor #1 to carburetor #2 by turning the synchronizing screw (3) in either direction until both gauges read the same. NOTE: After each step, rev the engine two or three times, each time for less than a second, and check the synchronization again. B.Synchronize carburetor #4 to carburetor #3 by turning the synchronizing screw (2) in either direction until both gauges read the same. NOTE: Turning screw clockwise raises carburetor #4 and lowers carburetor #3. C. Synchronize carburetor #2 to carburetor #3 by turning the synchronizing screw (1) in either direction until both gauges read the same. NOTE: Turning screw clockwise raises carburetor #3 and lowers carburetor #2. Vacuum pressure at engine idling speed is 37 kPa (280 mmHg). NOTE: The difference in vacuum pressure between two carburetors should not exceed 1.33 kPa (10.0 mmHg, 0.4 inHg). 7. Check engine idling speed. If out of specification, adjust. 8. Stop the engine and remove the measuring equipment. Yamaha then recommends the following. 9. Adjust: Throttle cable free play Refer to "ADJUSTING THE THROTTLE CABLE FREE PLAY". Throttle cable free play (at the flange of the throttle, grip) 4 - 6 mm (0.16 - 0.24 in) 10. Install vacuum plugs.
Freebird Posted March 20, 2007 Author #2 Posted March 20, 2007 Carburetor Syncing Thanks to Kenneth Branton (Kbran) for this excellent article. Thanks to George (kj5ix) for creating a .pdf file of this article that you may download and print. It is attached at the bottom of this article. First thing you'll want to do is get the bike warmed up and set your idle speed at 1000 RPM's. The next step is to access the four brass ports on the intake runners. They are located in the middle of the V ov the engine. If your bike is stock you will have two hoses and two caps to remove, one of each on each side of the engine. This is where you hook up the hoses from your carbtune II. I hang the carbtune from the right handlebar with the bars turned to the left so it is less likely to fall off. The next step is to hook up the Carbtune. I take the two hoses from the left side and route them under the carbs to the left side of the engine as you are seated on the bike. Left is seated on the bike and right is also seated on the bike. It doesn't matter which hose goes to what port. Take the two hoses from the right side of the Carbtune and hook them to the right side ports. Again it doesn't matter which port the idea is to have the left pair to the left cylinders and the right pair to the right cylinders. Another thing is don't worry about synching the carbs to get a specific vacuum reading. Just get them all even. Start up the bike and see what you have for a reading on your gauge. This is what mine looked like. If you need to do some adjusting here's what needs to be done. You'll want to adjust 1 and 2 on the left side and 3 and 4 on the right side of the bike (again, direction when sitting on the seat), These adjustments are made with a #2 Phillips screwdriver from the right side of the bike. Once both sets are done you will then synch the bank of 1 and 2 to the bank of 3 and 4. This adjustment is made with a regular screwdriver from the left side of the bike. Here is the adjustment screw for doing 1 and 2. It is accessed from the right side of the bike, looking through the V of the engine to the left side bank of carburetors. You will need a long #2 Phillips screwdriver to reach this one. It is located just above and left of the choke lever. Here is another picture. Go ahead and turn the screw a little bit in one direction. If the the carbs get more in synch, keep turning until it they are even. If they get farther out, you'll have to turn the screw the other way. Once you think they are good, rev the throttle or blip it a few times and see if they are sitll even. Once these two carbs are set it's time for the next two. Here is the adjustment screw for doing 3 and 4 (also accessed from the right side). Do the same here as the previous side. Once these two are set, it's time to synch the left side to the right side. \ Here is the screw for synching both sides together. It is accessed from the left side, just above the choke knob. This is a hex head screw with a slot for a screwdriver. When turning this screw you will see the left pair (1 and 2) move together as well as the right side (3 and 4) move together. Turn the screw which ever was is needed to get both sides even. Again blip the throttle and see if it stays. This is what I ended up with. Can't complain about that. Once everything is set shut off the engine and remove the synch gauge, reinstall your hoses and caps, and go for a ride. 2
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