Carb Sync - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 24 (permalink) Old 07-19-2008, 09:38 PM Thread Starter
 
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Carb Sync

How often do you have to sync your carbs ? What are the visible/audible symptoms of a carb out of sync ? Lastly, where can you buy a carb sync tool ?
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post #2 of 24 (permalink) Old 07-19-2008, 09:59 PM
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http://www.powerchutes.com/manometer.asp

Reverse order - here's a link to cheap, make-it-yourself sync tool (really works!); carb outta sync symptoms include rpms unstable and tach jumping; Clymer's recommends a carb sync every 3,000 miles or so - if you've pulled the carbs for any reason, however, best to sync 'em once you get 'em reinstalled.

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post #3 of 24 (permalink) Old 07-19-2008, 10:01 PM
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From the Verses, a rundown on synching, including a "how to know if you need to" write up-

Clicky-Clicky

As far as the tool, some folks make their own pretty inexpensively, or you could buy one at a variety of motorcycle tool/parts supply places. A Google search would get ya in the right neighborhood.
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post #4 of 24 (permalink) Old 07-19-2008, 10:24 PM
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I really hate to upset the statis quo here, but unless the bike is running rough and not holding an even idle, there is no reason to bother synching the carbs.

What you can do and requires not special tools is to make sure each thottle linkage begins moviing at the same time the other one does when you slowly twist the throttle.

The Vulcan uses CV carbs...which mean "constant velocity"...the diaphrams in each adjust to intake pressure of their respective cylnders, so synching the carbs is not really critical on the vulcan.

I had my bike for 5 years and never touched the carbs...and it ran fine.

Those with inline fours or bikes with slide type carbs should check the synch every 5 or 6 thousand miles.

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post #5 of 24 (permalink) Old 07-20-2008, 12:57 AM Thread Starter
 
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Thanks Knifemaker. I have 4300 miles on mine and was wondering that i missed the 3000 mark. Yet, i have no problems with carbs or rpm's or idle. Just curious if its a 'must-do' or do it when needed.
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post #6 of 24 (permalink) Old 07-20-2008, 01:53 AM
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I check and sync my carbs for peace of mind. It's not hard or costly and it does make the engine smoother if they are out of sync. My XS650 is real picky with carb sync, much more than our VN's

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post #7 of 24 (permalink) Old 07-20-2008, 02:11 AM
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Like KM said, the CV carbs aren't nearly as touchy to changes as the older carbs. As a side effect, they aren't as tuneable for High performance applications.

However, any time you optimize your carb settings, you increase mileage and efficiency.

No two cylinders are ever the same. Hence, no two cylinders flow the same. Syncing your carbs allows your carbs to feed the cylinders exactly what they need to do their job..

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post #8 of 24 (permalink) Old 07-20-2008, 10:38 AM
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I synced my carbs after I rebuilt them. I used a variation of the manometer. The benefit of this design is that the liquid can't be drawn up into your engine. It cost me ~$5 to make (two glass Starbucks coffee bottles, 2 rubber stoppers from Lowe's, 12 ft of 1/4" tubing). I used dexcool as the liquid inside, but you could really use anything. Because the Dexcool is much lighter than the mercury, it's more sensitive/accurate. The write-up in the Verses linked above is really good. I have pics in my gallery to go along with it if anyone needs them.

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Last edited by tilak; 07-20-2008 at 01:03 PM.
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post #9 of 24 (permalink) Old 07-20-2008, 11:41 AM
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Quote:
Originally Posted by tilak View Post
I synced my carbs after I rebuilt them. I used a variation of the manometer. The benefit of this design is that the liquid can't be drawn up into your engine. It cost me ~$5 to make (two glass Starbucks coffee bottles, 2 rubber stoppers from Lowe's, 12 ft of 1/4" tubing). I used dexcool as the liquid inside, but you could really use anything. Because the Dexcool is much less viscous than the mercury, it's more sensitive/accurate. The write-up in the Verses linked above is really good. I have pics in my gallery to go along with it if anyone needs them.

Peace,
Tilak
I really like the looks of this setup, but have one question...How do you measure the amount of vacuum...or do you just make sure both hoses are equal lengths, mark where the fluid level is with bike off, then start the engine and adjust the sync until the fluid reaches the same spot on each hose?
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post #10 of 24 (permalink) Old 07-20-2008, 12:59 PM
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The hoses coming from the carbs don't actually touch the liquid. They stop just below the rubber stopper. There is a much shorter hose that connects the two bottles that is submerged in the liquid. If the vacuum of one carb is greater, the liquid will flow into that bottle (lesser to greater). So you just watch which way the liquid is flowing and make very minor adjustments to the screw until it stabilizes. Turning the screw in increases vacuum in the rear cylinder carb; turning it out decreases it.

I hope that makes sense.

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