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post #1 of 15 (permalink) Old 07-29-2013, 07:52 AM Thread Starter
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Carb Synching High Idle video overview

Ok, I realized I had an extra carb so I wanted to figure out why my idle was so high after synching my carbs. Well, it makes sense if you watch the video. Also, I tested for air leaks and found none using propane and WD40. The propane thing is kinda scary yo.

Video is here http://youtu.be/Zc59BThqRa4

And so now, it's like, crappers, so in order to get the carbs to synch I have high idle, so how do I get them synched? Going to replace some spark plug wires and see if I that helps. Maybe I'm not burning enough in the front cylinder.

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post #2 of 15 (permalink) Old 07-29-2013, 09:19 AM
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First, I'd like to thank you for the video. Always wanted to see what that screw did.....

Next, I'll say this, and I know there will be folks here that will say I'm wrong, but I was always told that in this bike, because it uses CV carbs, the only thing you really need to "sync" on the carbs is to make sure both butterfly valves open at the same time when you crack the throttle. ("Butterfly Valve" is the term you were looking for in the video BTW)

I asked an actual mechinic at a Kaw dealer this and he said the same thing.
I remember "synching" carbs on a Triumph twin by pulling the air boots off and holding a mirror up to see if both valves opened at the same time...(helps to pull the diaphragms out)

Your vacuum diffrence might be do to a clog, a defect in the carb itself, or something else....

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post #3 of 15 (permalink) Old 07-29-2013, 09:24 AM Thread Starter
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Something else

Well, short of ripping the carbs off, I have no clue. I'll wait for cold weather before I get into that stuff. It rides pretty well now except for the slight vibration at 3500 up. I put some rubber in between the foot peg and the bike and that helps. It would make sense what you say about the valves opening at the same time and hopefully at the same rate.

I can't believe carb boots cost $25 bucks a piece! Man.

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post #4 of 15 (permalink) Old 07-29-2013, 11:17 AM
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In the video, the idle adjuster isn't touching because the throttles are closed tight.

Back off the lower throttle cable until you have about 3/16-1/4 " play. Start over.

got to go .
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post #5 of 15 (permalink) Old 07-29-2013, 12:02 PM Thread Starter
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Back off Lower throttle adjuster

It doesn't touch because of the synch screw pushing everything away from it. The throttle cable wouldn't do anything cause it's all the way loose (in the video there is no throttle cable so it's definitely loose.)

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post #6 of 15 (permalink) Old 07-29-2013, 07:27 PM
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ok, you are saying when the carbs are in sync, the throttle plates are too far open. You opened one before the idle got too high.

So, barring vacuum leaks the front throttle plate is sticking too far open. In order to sync, you then open the rear.

Unusual problem, but I think I understand.

If in your shoes, with no vacuum leaks, I would pull the carbs. I would look for mechanical obstruction to closing in the front carb. Gummy buildup, piece of dirt, throttle plate improperly adjusted on the throttle shaft, etc.

edit- before doing any of this, you may want to compression check both cylinders. Either cylinder poor could cause this.

Last edited by wmsonta; 07-29-2013 at 08:26 PM.
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post #7 of 15 (permalink) Old 07-29-2013, 07:43 PM
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Yes what he said^ ...... But are you saying the same "gap" exsists on the carbs that are on the bike?

Again I submit that synching the carbs is a somewhat useless endevor... As it only deals with zero throttle idle. If both butterflies open at the exact moment you begin to twist the throttle, that's all that really matters as engine demand will effect the rise and fall of the carb diaphragms.

Is there anyone that disputes this?

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post #8 of 15 (permalink) Old 07-29-2013, 08:17 PM
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Quote:
Originally Posted by wmsonta View Post
ok, you are saying when the carbs are in sync, the throttle plates are too far open. You opened one before the idle got too high.

So, barring vacuum leaks the front throttle plate is sticking too far open. In order to sync, you then open the rear.

Unusual problem, but I think I understand.

If in your shoes, with no vacuum leaks, I would pull the carbs. I would look for mechanical obstruction to closing in the front carb. Gummy buildup, piece of dirt. throttle plate improperly adjusted on the throttle shaft, etc.

edit- before doing any of this, you may want to compression check both cylinders. Either cylinder poor could cause this.
I also was thinking along these lines, but due to inexperience with carbs, I let the experts speak there wisdom & experience.


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post #9 of 15 (permalink) Old 07-29-2013, 08:59 PM
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I gotta ask, how bad is the vibration when you feel it? Is it bad enough to shake mirrors? If so, I would be concerned your balancer dampeners are going out.

Here's a quick test you can do w/o the bike moving down the road. Put your bike on center stand on a smooth concrete floor, turn it on and let it warm up (skip this if already warm), then start cranking the throttle to where you feel the vibes and watch to see if the bike moves around the floor. If it moves a lot, then again I'd be concerned about your balancer dampeners.

Before I had the balancers replaced, my 750 had bad vibes in the pegs and mirrors at around the same RPM's.

I could be wrong, but the sync adjustment shouldn't affect the carbs beyond off idle / slow cruise. Beyond that, both should be getting enough air to where the sync doesn't matter anymore. Again, could be wrong on that analysis.

I only understand what I don't understand.

Last edited by blazblu82; 07-29-2013 at 09:18 PM.
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post #10 of 15 (permalink) Old 07-29-2013, 09:16 PM
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Quote:
Originally Posted by blazblu82 View Post

I could be wrong, but the sync adjustment shouldn't affect the carbs off idle / slow cruise. Beyond that, both should be getting enough air to where the sync doesn't matter anymore. Again, could be wrong on that analysis
The sync will affect the entire pilot circuit. The first 25% of the throttle, 90+% of all your riding. I now run 60-65 mph @ 1/4 inch of throttle.

These people are right, no discernible difference in WFO. Do not have mpg yet, I expect little change. Dunno.

The intermediate circuit does not 'see' vacuum until the end of the pilot circuit.
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