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Carb sync Qs: bolts, lines, adapters, whys? (and happy NY! :-)

6942 Views 11 Replies 4 Participants Last post by  theGruvedoktor
Hi everybody,

After successfully servicing my wife's Ninja 250 (plugs, valves, carbs sync'd, coolant, oil/filter, etc...) I decided to go for it on my 2000 R1.

While I think I understand the procedure (it's not that much different from the Ninja - same principles!), I'm having trouble to "get to stuff". Of course, I'm a relative newbie when it comes to mech work, so please forgive my n00bie questions.

First things first: got the seat/tank removed, and external fuel line hooked into the fuel filter. Everything is set, bike runs fine like this.

Now, I need to remove the bolts to hook up the adapters (from my Carbtune), and then the vacuum lines to them. There's 4 of them. Well, make that 3: it seems the leftmost carb has a "built in" adapter with a hose clamped to it.

Problem number one: how to get this hose off? I've been able to take the clamp off, but I don't manage to break the hose loose. Is there any trick?

Problem number two: the other bolts are somewhat accessible. Not great, but doable. However, I'm afraid of having the bolts fall off as soon as I unscrew them. Any tricks to keep them from falling? (I've hear saran wrap helps?). Magnets? Spells?

Problem number three: the adjustment screws are a pain to get to. First I used a mirror to find them (dentist mirror, about half an inch diameter), then I was able to reach them with a long bit. A hint/tips thread on this forum recommended to put the screwdrivers in place (on the 3 of them) before you start the procedure. That's a great tip so you don't have to fight to find them again as the bike is running, but it means they have to be held "upside down". Gravity wants to get them to fall over, so is there any secret to keeping them hooked up?

Last (but not least): given that it's a PITA to get to the sync bolts, I suppose I should take the opportunity I have and put some "permanent" adapters. How well do they work? I went on the Carbtune website and they seem to be gone. I'd prefer those that come with some length of hose, so I can easily hook up the carbtune to them next time around.

And a question! Why does one of the carbs have its vacuum line hooked up? Where is it hooked to, and if the bike runs ok without it, why is it there in the first place?

As you see, many questions, many doubts... and lots of skin lost on my hands already.

Any help would be really appreciated.

Thanks in advance.

Cheers, and happy new year!

-- Greg
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The one cylinder with a vacume hose on it runs the AIS system.

You can get the adapters from Parts unlimited. They work well, and make it allot easier as you have found.

Dipping the end of the socket in grease before you remove the bolts can help.

Take the air box off, it makes it a bit easier to see, and does not need to be installed to sync the carbs.

Need one of the cheap jewlers screwdrivers to adjust the carbs, and even them they are a pain to get to.

The rubber hoses can get fused to the metal pipe, but if you use pliars and spin the hose on the pipe it will break it free.

The carbed R6;s have neat little aluminum plugs that connect their sync ports to one another. You can buy the adapters for the three cylinders that dont have them, then add some 5 or 6 inch rubber lines to each of them, and use the r6 plugs to connect them together.

Plus this will be the perfect time to disable the AIS system.
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re carb balancing


thought you all might like to know of an alternative to the standard carb stix most people tend to use for balancibng carbs.

the bit of kit i use is a flow meter held in the opening to each carb that then gives vacumn/flow rate readout on a graduated scale,makes balancing a 5 minute job once you have the tank and air box stripped off the bike much easier than installing hoses/adaptors of any type and just as accurate as i have done a back to back comparison with a morgan Carbtune (stix) on my own bike and both gave the same reading back to back.

i have tried to attach a picture of the flow meter i use hope it can be viewed.
i got my from Demon tweeks here in the u.k it can be found online on their motorsport pages...

hope this helps




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Hey Dave,

That's a great tip. It certainly looks way easier than hooking up to the vacuum ports (at least on the R1 - it was not so hard to do it on my wife's Ninja 250).

Do you hook up 4 of them at the same time or do you move one across all carbs and write down the reading on each?
Seems like the latter could be doable and would be cheaper, but a little bit of pain in the butt to make sure everything is all sync'd (you have to go back and forth). I'd rather have the readings move while I turn the screws so I can adjust precisely. Maybe you can get away with just 2 since you always end up balancing 2 sets. They're not too expensive anyways: I'd probably want to go with one on each carb as I turn the screws.

Do you find that the readings are accurate enough on those things?


-- Greg
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re flowmeter

Hi To answer your questions yes the accuracey is fine as originaly this was developed by an engineer at weber for balancing their carbs mainly for Car application but works just as well on bikes.

gave me exactley the same reding as my carb stix and manometer gauges i have used in the past.
i always take a reading from the reference carb as a starting point generaly the one that is adjusted with the idle screw,then move across with the gauge to the next carb and sync to the same value as the reference continue till all carbs have been adjusted to same value then simply place gauge in bellmouth of each carb for about 5 seconds to take a reading and check they are all even after adjustment.

really is just as accurate and a lot quicker than any other method i have come across for balancing carbs/throttle bodies.

i was intorduced to these through Rhencullens my local dyno shop here in the u.k where there mechanic had been working on top flight race bikes using it for years with no problems.


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Hi Dave,

Thanks for all the hints/tips. Sounds like I'm going to get one of those! :)

I found this online reseller that carries them: http://www.cbperformance.com/catalog.asp?ProductID=572

Which one do I need? Seems like the SK version covers a wider range of diameters (40 to 55 mm instead of 48 to 53 for the BK), so I'm not sure why anyone would want the BK? Are there cases where the SK doesn't work?

TIA. Much appreciated!

-- Greg
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re carb flow meter

Hi thanks for the response reference to the flowmeter i posted up.

in short i wold have to say that both the items you found look exactley the same although they quote diffierent sizes.
my advice would be just to measure your own velocity stacks/inlet rubbers for the application you wish to use the flowmeter and see which size is best match.

the one i bought from demontweeks here in the u.k was just one size think it will go as big as 54mm which would probabley be too small for large v-twins such as aprillia mille's or ducati's so then you would possible need the larger size flowmeter/adaptor as you info doesn't say if the rubber nozzles are to be interchanged between the standard flowmeter or not.

if the rubbers are interchangeable i would probabley buy both myself to cover all future prospects as under $50 doesn't seems that much to me think mine was about ?45 when i bought mine.


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Thanks Dave. I ordered the stuff a few minutes ago, so I hope I'll get it before next weekend so I can play with it. :)


-- Greg
Sync'ing is done! Thanks Dave for the piece of advice, it made it so much simpler than hooking up the vacuum lines!


-- Greg
re carb synching

Hi thats great news glad you found it usefull.

i used to find that there was enough fuel left in my fuel lines for me to check my bike was synced each time i cleaned the arfilter and only needed to hook up to a jug of fuel if they needed adjustment.

like i said it really does make balancing carbs /throttle bodies a 5 minute job once you have the tank off the bike.

glad i could be of help...


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So, where are these elusive bolts that have to be removed to hook up the adapters?? I was going to do a carb sync this weekend and the only bolts that I saw on the carbs that could be removed (that were relatively close to the cryptic picture in the service manual) were the brass ones at the bottom that empty the float chambers...
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