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how to synchronize carbies

Old 05-15-2008, 05:08 AM
bluebeard's Avatar
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Default how to synchronize carbies

I regularly find people asking how to balance their carbies so I thought I'd do a write up. I hope the pictures work as I can't see them in the preview. I'm not a mechanic but I have been doing it for a long time on several bikes. Each bike has it's own personality which dictates some of the finer points but the basic method is the same for all. At the end of the day the more you do it the more you will understand your bikes personality & what works & what doesn't.

Firstly the only special tool required is a balanced set of gauges. Either dial or liquid work fine. I use gauges as they are more robust & don't rely on having exact amounts of liquid. You will see in the pictures that mine are old. I mean real old. Rusty, broken glass etc. They have even been in a high speed car rollover & bounced down the road. They were calibrated & good as new. To business.

Make sure the bike is on the centre stand or similar. Remove the seat & fairing etc & raise the tank all enough to give access to the carbies. I personally disconnect the prop stay from it's slider & prop it on the carbies. It lifts the tank higher & allows just a bit more room.

To do the job properly you must clean & gap your plugs, check the air filter & make sure the valves are adjusted correctly.

Remove the rubber caps that block the vacuum ports being careful not to break the rubber or drop a circlip. They are hard to find if dropped.

Connect the four gauges to the four vacuum ports & start the engine. Whilst it is warming up adjust the damper valves so that the needles are fluctuating minimally yet able to respond to the smallest amount of vacuum variation. If they bounce too much or can't respond because they are too tight incorrect readings will be the result. One of the carbies will not be adjustable. It is the base by which the others are set. On my old Hurricane it's no2.

Once the motor is up to running temperature set the idle to factory spec. Usually 1000-1100 rpm. Then with a Phillips screwdriver or what ever tool your bike requires adjust the carbies by the screws on linkage that joins all four gradually until they all have the same reading on the gauges.
What the reading is doesn't matter. Keep an eye on the revs & constantly return the idle back to spec. Also keep an eye on the temperature. If the bike gets hot turn it off & allow it to cool down. Once you have done this the bike should idle smooth & run with a lot more power & rideability.
Like I said. Basic & really quite simple. Remember that there is no need to touch the pilot air screws. They are the ones that screw into the carbie body.




Old 05-15-2008, 05:37 AM
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Default RE: how to synchronize carbies

Thanks for posting this - I need to do it. Much appreciated.
Is there any relavance to the blue circle on photo 4?
Old 05-15-2008, 06:09 AM
bluebeard's Avatar
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Default RE: how to synchronize carbies

Thanks. I did something wrong adding the pictures so they aren't where they should be.[sm=oopssign.gif] The circle in pic #4 is where I put the prop stay. The blue circles in pic #1 are the rubber stoppers on the vacuum ports. Hope it helps.
Old 05-15-2008, 09:14 AM
Shadow's Avatar
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Default RE: how to synchronize carbies

Thanks, Blue Mate - great writeup. I'll have a go and see how it comes out........
Old 07-02-2008, 04:36 AM
Join Date: Jul 2008
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Default RE: how to synchronize carbies

Another option for those of you like that are too cheap to buy a manometer is to make your own. The vacuum guages bluebeard used are a lot cheaper than a manometer but I still prefer to spend as little as possible on specialty tools that won't get used as often.

Here's a list of what I used to make mine.

50 ft 3/8 inch clear vinyl tubing
2 3/8 inch compression 'T's
2 3/8 inch compression elbows
1 yard stick
and a bunch of zip ties
some extra oil or transmission fluid

Maybe a total cost of $15

You need to cut your 50 ft of tubing into four pieces roughly the same size 12 1/2 ft. Connect all four using the 'T's and Elbows at one end. Line up the four tubes with the connections at the bottom on your yard stick and zip it all together. Mark a spot 16 inches from the loose end of three of the tubes. Stick those three in a quart of oil and suck on the fourth untill your oil reaches the 16 inch mark. Once you get it to that mark you need to hang all four tubes above the yard stick and wait for it to all balance out to 12 inches in each tube.

After Sir Isaac Newton's law of gravity levels out the oil you can hook up the four tubes to your vacuum ports and balance the carbs against each other.


If your carbs are really out of whack you'll have to keep an eye on the oil levels and keep your thumb near the kill switch so you don't suck oil straight into your carbs.

From my own personal experiences, the oil won't hurt them but it is a pain with all the smoke and you have to run the oil out before you can get a good balance again.

Hope this Helps someone out there save a buck or few hundred from servicing at the stealerships.
Old 07-08-2008, 12:58 PM
Join Date: Jan 2008
Posts: 76
Default RE: how to synchronize carbies

@B Evil:

Could you post a few pictures or the parts you used and the finished product? I've never heard about a 4port home-made sync-tool...until now.

Also, what did you use for adaptors between the tubes and the vacuum ports?
Old 07-18-2008, 05:44 PM
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Location: Cincy, OH
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Default RE: how to synchronize carbies

on my cbr f4 the only candidate I can see for attaching the hose is the small hose that comes from below the carbs and goes into the air box, I don't see any vacuum port to hook into on these carbs
Old 10-11-2008, 07:11 AM
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Default RE: how to synchronize carbies

See myCARB SYNC BALANCE - CBR1000F - using guages and Morgan Carbtune Pro.

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