Author Topic: Carburettor synchronization Questions  (Read 12847 times)

Offline Red01

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Carburettor synchronization Questions
« on: March 12, 2005, 01:51:58 AM »
Carburettor synchronization Questions
 Hi Everyone,
The other day my bike mechanic said my carbs were out of synch. He fiddled with some screws between the carbs... He would not say much about what its all about? As far as I was concerned, the bike was fine and still is. Gains power beautifully on the throttle, only seems to take a lot more gas than before my Blackbox blew.

I need to know what this synching thing is and how to go about it. I love to do everything myself. I'm going through with getting myself a manual currently hoping it will of help but before then here are some dumb questions for you guys?

What are the signs that carbs are out of synch??

How do you synch carbs?? Do you need special tools or gauges? I have no access to any such tools or gauges, so how can I improvise?
How often do you do it?

Please help!
(8/11/03 9:43 am)

 Synching makes them all function at the same level. You have a bank of 4 carbs and if one is putting out more gas, the engine runs rough.

It is an easy adjustment, but does require the use of vacuum gauges.
(8/11/03 9:37 am)
Re: Carbs

 Usually with an inline 4 you'll use a special 'rack' of either 4 dial type vacumn gauges, or 4 mercury type (Like a thermometer) vacun gauges.
The mercury type run about $40 USD up.......Dial type run $60-$200 USD.

From what i understand, using one vacumn gauge is possible........but a set of 4 is easier, and quicker.

Haven't synched carbs in years..............(Did it a couple times on a cb 750)
I bought a set of Emgo vacumn gauges recently.......around $
I'm not 'endorsing' them since I haven't used them....yet.

(8/11/03 10:45 am)
Re: Carbs

 I've thought about this recently. Has anyone gotten a B12 synced, or seen first hand that the carbs were "out"??
2 years and 16K miles on mine, and I think it runs fine, but I would be curiouse to hook it up the a 4 gage rack and see what it says.
(8/11/03 11:04 am)
Re: Carbs

 Hey.....I've got my cheapies in the trailer. If you come to the september yourself!

I bought a set of 'Honda' gauges in '75........they were $75!! A lot better quality than these Emgos.......but for $50.....I thought I'd give it a shot.

I think it's a normal 'occasional' adjustment...........usually part of a major service. With the old 4 into 4 pipes, you could get an idea of how close/bad they were by holding your hands over the individual tailpipes.....and feeling the exhaust pressure.

Danger! You have just reached the limit of your carb synch knowledge! Proceed at risk of embarassment!
(8/11/03 11:53 am)
Re: Carbs

 You should synch the carbs each time you adjust your valves clearances.
This is to ensure the vacuum causing the slide to lift is the same on all 4 carbs.
Once you change the valve clearance the vacuum may change also a bit, as the flow parameters/restrictions may change.
The synch should be done if you separate the carbs for cleaning.
The carbs are synchronized at ca. 1.7-2 krpm which is just above the tickover (idle speed).
This ensures smooth transition between idle and low revs when pulling away.
You should be able notice the difference between smooth and rough running on the same bike, but usually you don't remember how it was before;-)
Besides all carbs I've seen when doing synchro where ok at the point I synchronized them but out of synch at idle or higher revs, and it IS normal.
So if you always pull away at 4 krpm and more don't care about it;-)
IMO it is not so important, I mean if the engine is pulling ok and running smooth, I wouldn't bother.
I know this 'cause I bought vacuum gauges and done it;-)

And I don't think you would notice any differences with 4into 4 exhaust by putting your hand over the pipes;-)

BUT, if the engine is using much more gas after the service then before, something must be wrong (fuel level, pilot screw position, needle position, clogged air passage etc) and the carbs should be examined.

(8/11/03 2:55 pm)
Re: Carburettor synchronization Questions

 i prefer to use one gage.
this eliminates the need to calibrate the individual gages.
i once made a manometer using mercury, but that is probably difficult to buy now.

it is really only the idle that matters. you want all 4 slides to start rising at the same time, so they should all have the same starting vacuum at idle. also make sure that the cables all start pulling at the same time.

make a big difference when all the carbs are working together rahter than against each other... But with b12 power, only a rough idle will be noticable.
(8/11/03 7:52 pm)
Any time there is more than one carb

 syncronization is an issue.

Yes, first hand Manny. It makes a difference in engine smoothness, gas mileage, throttle response, all the good stuff. The B-12 is such a beast that it would have to be fairly screwed up before you would probably notice. Especially since the change from synced to otherwise happens over time, it sort of sneaks up on you. Where you would notice it is your first ride after the sync has been done.

The bandits use a split rack - you sync 1 to 2, 3 to 4, then the pair 1 -2 to 3 -4. It takes a little patience and a little getting used to, really not too bad. It needs to be done with the engine fully warmed up, but not overheated.

I prefer to use the "carb stix" type sync tool. They suit me, cheap. All four tubes share a common mercury source. If you use the same restrictors in the four vacuum lines to dampen the sensitivity (so you don't slurp some merc into your beast) the relative calibration between the four "channels" is not an issue. If you use one guage, there is the question of the considerable interaction between the carbs that is very clear when you monitor four simultaneously. There are good vac guage setups available, I have worked around too much test equipment to have blind faith in the guages being calibrated equally though, and sure don't want to mess around cross checking guages or pay for a cert.

With a four into one exhaust with header crossovers you might as well slaughter a chicken under the full moon as try to determine the state of tune from your exhaust pulses. I feel about the same way about someone givin the ol screws a twist and assuring me that it's alot better now.

IMHO this is just like your valve adjustment. Get the tools, learn how, enjoy more. But just like the valve adj, it needs to be done.

(8/12/03 3:07 am)
Re: Any time there is more than one carb

 Cheers Guys!
I am overwhelmed by the detailed knowledge out here!!!
Thank you all for the help! 'Guess I need to get myself a set of gauges, a can of beer and a whole day out of the office
I hope when the manual comes it'll make me as knowledgeable as you lot.
2001 GSF1200S
2010 Concours 14ABS