Carburetor
Carb Synching
When Do I Need To Synch My Carbs
This is a procedure that needs to be done at least once a year during maintenance, any time you remove and replace the carbs, or a least any time your bike feels like it running rough. Very easy to do, and very inexpensive.
Another view: -- Rules are:
-- synch whenever you make major change to the air/fuel/exhaust systems
-- synch whenever you start to feel new vibration in the grips or your mirrors start to vibrate
Otherwise - you can always follow the service recommendation
Note: Not only is this a procedure for when you jet, it should be done each time you adjust the carbs, and anytime the bike starts to run roughly.
Carb Synch Made Easy
Manometers or Synch Gauges are relatively inexpensive to purchase, but it's easy to make one. A tachometer is not optional, it is a "must have" tool to do this job.
Build your own Manometer links..
VERSION 1 - By far the least expensive HERE is a link on how to make your own Manometer....DON'T USE WATER IN THIS!
NOTE: The 1100 uses 3/16" hose not 1/8" as mentioned in the link. The link is a universal DIY.
VERSION 2 - Makes it more difficult to suck indicator fluid into the bike, my preferred style HERE..... DON'T USE PLASTIC BOTTLES! Kind of a "no brainer", but some have actually tried it.
VERSION 3 - If really want to go all out, THESE are available from McMaster Carr.. and the rest of the instructions..
~Quoted from original source~
1. Vacuum gauge - like mentioned above
2. 1/2" Female- 1/2" female coupling
3. 1/2" male - 3/16" nipple connector
4. 3/16" ID clear tubing (one end is darker due to staining from oil)
5. Old pilot jet for vacuum restrictor (helps to reduce the gauge needle from bouncing too much)
6. Plastic 3/16" connector to connect to vacuum tube from the carb. I filed down the ring shank to make removing it off the bike tube easier.
Obviously you'll need 2 of these. The length of tubing is up to you. I have about 6' on each. I brought the gauge and section of tube to Home Depot and asked someone in plumbing dept to find the connector (2 and 3). Wrap the threads with Teflon tape and just screw them together tight.
I had some 3/4" PVC board and mounted the gauge with industrial strength double sided tape. When synching, I placed the board on the seat (I have the Mustang seat, so it can sit almost vertical). Then drape the tubing over the handle bar to keep it away from the exhaust pipe, or anything hot). The 6' length gives me plenty of room to connect to the bike.
...A note from Sick Mick...
your carbs is a very simple process. Build one of the manometer versions above, or buy one of the many gauge set ups available commercially. Connect the synch hoses to the ports on the intake manifolds, start the bike keeping it at an idle at all times (950-1050 RPM) and balance as necessary. The bold note below will tell you which way to turn the screw. (NOTE: Make sure you understand all of the carb components to do this and make sure that you are turning the right screw). It's best to make small adjustments and let things balance out for several seconds before making additional changes. Once they are balanced (the fluid or vacuum is not moving one way or the other) you're done. Put your tools in your tool box and have a cold one. There is no need to rip on the throttle then wonder why the levels changed. Save your brain for something a little more important. Remember, this is a very simple process.
An important tip.....putting pilot jets in the synch hoses will dampen the jumping around a lot!
A note from Dro...
Don't over think it -- you set them in sync at idle so they work together appropriately when you take off, when you first twist the throttle you want both carbs to open at the appropriate time time, as you increase in rpm they will not stay in sync because both intake valves are not opening at the same time obviously and the more rpm you have the more the vacuum changes and the valves open and close faster......same in a car with multiple carbs, when you mash the gas pedal you want the carbs to open at the same time not one and then the other....
Everybody puts way more emphasis on the carb sync than they need too - it is not an exact thing and never will be at any rpm, you just want it as close as possible.........they even give you an acceptable range of difference between the two at idle........ don't over think it.
"Reminder for DIY Manometer: Turn the synch Screw Clockwise (in) to lower the oil level for the rear carb" ...and always remember to turn it SLOW in small increments and let everything settle before turning it again. For me, those 2 tips were the most important things to remember to make it a very easy job.
Synch Screw:
Front Port:
Rear Port:
The BENCH SYNCH From Tim B - Metric Magic
"With the carbs out of the bike hold them up to a light and look down the throats. Take a sewing needle or something of that sort and bring the idle screw down until the needle will barely slide underneath one butterfly (try and remember how many times you turn it so you can get it back to where it was when you're done). Then take the needle out and check the other butterfly. Adjust the synch screw to get both butterfly's where they are even. This will get you very close to synched. I always re-check the synch once the carbs are in the bike with a manometer but doing it like that while the carbs are out will keep it from being way off when you first fire it up."
Pin/Needle Method:
1. Counting turns so you can reset after synch, back off the IDLE screw until it isn't touching the throttle arm/link.
2. Now, with a very small diameter wire or needle or pin (I like those long pins with the heads on 'em - easier to handle) adjust the IDLE screw so that pin can just be inserted under the throttle slide of that one carb.
3. Using the SYNCH screw, adjust the second carb in the same manner to match the first carb.
4. Reset the IDLE screw to original position.
Pencil/Light Method:
1. Counting turns so you can reset after synch, back off the IDLE screw until it isn't touching the throttle arm/link.
2. Back off the SYNCH screw until it isn't touching.
3. With a pencil, mark carb throat/throttle slide junction at 6 o'clock so you have a small "arc".
4. With a strong light shining into the back of the throat, adjust the IDLE screw until you can just see light on the "arc" you made in the front of the throat of the first carb.
5. Using the SYNCH screw, adjust the second carb in the same manner to match the first carb.
6. Reset the IDLE screw to original position.
Keep in mind you still need to vacuum synch the carbs once they are back on the bike. the bench synch is merely to get you close to get the bike running.
Synch Screw Modification For Easier Carb Synching - from Maustarman
Getting into the carb synch screw for adjustment can be a tight fit causing burned fingers and a few 4 letter words. Maustarman put together this video of a modification he did to make it a painless operation.
Carb Synch Screw Modification "How To" Video
Carb Cleaning
- If the bike has been sitting, drain the fuel from the float bowls before starting. This will help prevent sucking the gunk into the jets. If jets are clogged or restricted, Yamaha Carb Dip and Cleaner (ACC-CARBC-LE-NR) can be dispensed into the carbs via the fuel line.Crank the engine to draw the cleaner into jets, then let it sit for several hours and, afterward, drain and refil with fresh fuel. this process will work if the carbs aren't badly clogged. You can repeat the process, allowing the cleaner more time in the carbs or disassmble the carbs for direct cleaning. (The Yamaha Cleaner is safe for plastic and rubber parts, unlike Chem-Dip and other cleaners)
- Put a liberal amount of Seafoam or Berrymans in the tank. A half can in a full tank of gas is a normal amount.
- The Right Way - Pull the cabs, clean completely with carb cleaner, including removal of all jets, cleaning of all jet seats, valve seats, etc. Be careful to not use on rubber parts (O-Rings, Diaphragms, throttle shaft seals etc.)
- See the Tuning page for details on carb dis-assembly or consult a shop manual. (You do own a shop manual for your bike, right?)
Carb jetting information is in the TUNING section or click here > 6 Carb Jetting
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"The Over Complicated Synch Method".... below. You can do all of this if you want, but the easiest method is listed above. Left here for reference.
Daddo (DaddoCFL)
V-Star 1100 Carburetor Synchronization process
In order to properly synchronize the carburetors on your engine, your valves really needs to be set to their correct tolerances. And the engine idle speed should be set to it’s correct range. I keep mine right in the middle of the 950 to 1050 rpm suggested by Yamaha.
The manual suggests that the bike be placed on a suitable stand or lift. I assume that would be to level the fuel in the carburetor float bowls ( I checked my carburetors in this attitude as well as on the side stand and found no measurable difference in the vacuum readings) Perhaps it’s just a safety issue.
Ok, You will need to remove the Seats and Fuel Tank in this order:
1. ) Passenger Seat – Single Allen head bolt.
2. ) Seat Bracket – (not necessary on Classic.
3. ) Riders Seat – Single Allen head bolt on a Classic, the Custom’s seat was held on by the seat bracket
4. ) Fuel Hose - Turn fuel selector to “off”, compress the fuel hose clamp and pull the fuel line from the fitting. Keep a wipe rag under the line as some fuel will run out.
5. ) “Igniter plate” ( Spelled Ignitor in the manual) This assembly, with a rectangular electronic module on it is held on by three (3) “quick fasteners”. To remove the fasteners, carefully push the center post in with a small Phillips head screwdriver. Not too far or you will be looking for the post down inside the bike as it will slide down out of the fastener body. There is no need to remove it from the bike, but it must be loose to access the Speedometer lead connector. (to reinstall the fasteners, you must push the post back up through the body of the fastener until it extends far enough up from the fastener top to allow the body to compress. Insert the fastener into the hole and depress the post to where it is flush with the fastener body.
6. ) Mud Guard – The Igniter Plate was mounted to it on the Custom
7. ) Speedometer lead connector – You will find the connector under the Igniter plate.
8.) Remove the Fuel Tank. – Two bolts, on both the Custom and the Classic.
9. ) Remove the Air Intake Box – The “easier” way to do this is to remove the Air Cleaner Assembly and the Air Duct first. The Air Intake Box is held in place by a hose clamp on each Carburetor, another on the top end of the Air Duct, and another on the breather hose that comes out of the front cylinder head.
10. ) Remove the two vacuum plugs. Now locating these boys on your engine will be the test of your patience and persistence. The carburetor vacuum ports are on the ducts which leads from each carburetor into the cylinder head. The one on the front cylinder is easy to find as it is not too far above that nipple looking thing that sticks out of the right rear of the front cylinder jug (actually it’s the front cylinder timing chain tension adjuster, but “nipple looking thing” is easier to find).
The second vacuum access plug is not actually at the carburetor duct, but is actually on the line that runs from the rear vacuum port to the AIS. that hides in the storage compartment of your bike. Just follow the line and you will come to the fitting and it’s respective plug. Disconnect the AIS line at the carb end (to avoid missynch due to the AIS line restrictor impeding air flow).
- Measurement Process
1. ) Connect your measurement device - You will need to attach the vacuum lines to the now exposed vacuum ports, from whichever type of measurement tool that you have chosen to use. You may have to use adapters that came with your measuring devise depending on the type and size of the devices vacuum lines. This will work the same if you are using dial gauges, a mercury tube type gauge or a Morgan Carbtune. Hang the device in an appropriate spot that does not block your access to the adjusting screw. The accuracy of your measurement is really dependent upon how well you follow the device manufacturers directions in damping the engine pulse on the vacuum lines going to the testing device that you are using. All directions will differ slightly but the goal here is to restrict the flow of air in the test lines to the point where the relative vacuum can stabilize, but the flow is so restricted that it will negate the violent pulsing of the indicator. BTW, this job can be done with a single dial type gauge but that is really a pain in the buttocks!
2. ) Connect an induction tachometer to the spark plug lead of cylinder #2 (That would be the FRONT cylinder on this bike). Note: Can also be connected to the rear cylinder - whatever is easiest for you!)
3. ) Start the engine and let it warm up for a few minutes. Now this is an issue for you to consider, and a choice for you to make. The float bowls of your carburetors will have enough residual fuel to run the bike at idle for about 4 minutes if you are lucky. This is more then sufficient time to sync the two carbs, but the engine must be HOT to get accurate readings. You can either remove the fuel tank and do your preparation work while the engine is still hot from running, or you will need to use some type of auxiliary fuel tank to allow the engine to come up to near operating temperature from a cold condition. A lot of motorcycle supply houses sell small plastic remote fuel tanks that hold a liter or so of gas, or you can salvage a tank from a discarded lawn mower and use that as I did.
4. ) Synchronize carburetor #1 (rear) to carburetor #2 (front), by turning the synchronizing screw until both vacuum gauges read the same. That screw can be found between the V and just under the carburetors. On the left side of your engine, you will find a chrome carburetor cover. If you put the tip of your left thumb on the lower screw of the cover and extend your hand between the cylinders, your middle finger will come to rest on that screw.
The difference between the two gauges should not be more then: 1.33kPa (10 mmHg).
And the reading at idle should approximate: 34.7 – 37.3 kPa (260 – 280mmHg)
5.) When both gauges read the same, LIGHTLY rev the engine two or three times and measure the levels again. (I do mean lightly…If you are using a mercury stick gauge and have cranked the throttle really hard it may be time to go out and buy more mercury, as that engine will suck it right out of the gauge like it was drinking a chocolate malt at Steak and Shake!)
Button it up! It’s a done deal! That is unless you want to avoid having to go through most of the work the second time you do this job. If so, keep reading.
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Note: Damping the fast movement of the measurement liquid in the DIY manometer columns:
- Vacuum line restrictors can be purchased in your auto parts store
- or, for performance modified bikes, insert the old / stock pilot jets into the hose ends of the manometer
- far enough to allow insertion of the connector below the jet.
Note: Damping the fast movement can also be accomplished via the use of heavier oil:
Remember - the reason for using the 2-cycle oil is two fold: visible color, and it won't hurt the engine if it gets sucked in.
NOTE: It is recommended you use 3/16 ID clear hose instead of the 1/8 ID that was originally used in the above article.
Reasons:
a.) will cause less "bounce" when measuring/synching - larger ID means more fluid / weight to move therefore less "bounce",
b.) 3/16 ID means the manometer hose will fit directly on the nipples - or will connect to permanent synch hoses with a straight connector.
Either size will do the job, but 3/16 is better!
Throttle Shaft Seal Replacement
We have found that a Yamaha part number 256-14997-00-00 seal is a perfect replacement for the throttle shaft seal on the 1100's Mikuni carbs. Thanks to 09alex1977 for researching this. More info available in the link to the forum thread. 8mm ID X 11.5mm OD
Forum thread Throttle Shaft Seal Replacement
Carb jetting information is in the TUNING section or click here > 6 Carb Jetting