Carb balance issue - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 7 (permalink) Old 11-03-2011, 01:26 AM Thread Starter
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Carb balance issue

Any thoughts about a carb that pulls more vacuum on the rear cylinder with throttle than the front?

I have used my yardstick manometer to adjust my carbs at idle, but when I give a little throttle the rear pulls the oil 2 or 3 inches higher for the rear. Is this a sign that my jets need to be pulled or should I look at my linkage?

Another thought I had was air cleaners, but they both feed the common air box correct?

Bike is full stock, 2003 with 6,200 miles, bike sat much of the past 2 years with PO, new NGK plugs, front ACCT rebuilt, Compression: 155 Front, 160 Rear.
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post #2 of 7 (permalink) Old 11-03-2011, 09:05 AM
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You are correct about the common air box. As for the jets, one could be partially clogged. I wouldn't hurt to check them. You can get to them without removing the carbs but it's a bit challenging. Still quicker than removing the carbs.

I know when I sync'd mine I upped the idle with the idle adjustment knob. It's the black one on the left side (sitting) found at the carbs. Turning it up some allows you to adjust with more throttle & keeps your hands free.

There's my 2c worth.
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post #3 of 7 (permalink) Old 11-03-2011, 09:53 AM Thread Starter
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Thanks K69.
I figured as such and I like the idea of checking the jets w/out pulling the carbs. I had pulled the tank last month, but didn't venture below the airbox.

I've got some seafoam in the tank hoping to unstick something, maybe a slide or crud somewhere. Have also drained the bowls a couple times and got some pepper like stuff out.

Good idea with bringing the idle up with the adjusting screw, reduces variables.
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post #4 of 7 (permalink) Old 11-03-2011, 10:39 AM
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Carb balance is really only important at idle under high vacuum conditions. As you roll off idle, the size of the opening gets so large that small variations from front to rear are minimized. If you have them balanced at idle, you are all set.

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post #5 of 7 (permalink) Old 11-03-2011, 10:59 AM
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Quote:
Originally Posted by 93VN750 View Post
Carb balance is really only important at idle under high vacuum conditions. As you roll off idle, the size of the opening gets so large that small variations from front to rear are minimized. If you have them balanced at idle, you are all set.

Jon
This is good to know. I was having the same issue as Tim.

I'd have it balanced at idle and then it'd change as I gave it throttle.

I think KM mentioned in another thread that this isn't as big of an issue on these bikes as the CV carbs will adjust fuel flow depending on vacuum.

I should have done a video of the manometer set-up.

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post #6 of 7 (permalink) Old 11-03-2011, 12:40 PM
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Quote:
Originally Posted by Roach View Post
I should have done a video of the manometer set-up.
That can be your next one!

I know when I did mine I was pretty balanced thru throttle. Maybe I just got lucky? It wasn't off by much but I definitly didn't have a 2" to 3" difference.
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post #7 of 7 (permalink) Old 11-03-2011, 11:08 PM Thread Starter
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The 2-3" diff. is better than what I was getting before changing the front ACCT spring. and putting a few miles on it with a good concentration of seafoam in the tank (about 5 oz/half tank)
I'm hoping things get even better once I get a chance to really ride it. I just refilled the tank from about 1/4 and added a half bottle of Chevron injector cleaner. We'll see how this does.

BTW, my manometer is simple.
1/4" clear tubing looped under a metal yard stick with a plastic covered metal hook that I took off a little cargo net for my Ninja. I use the hook to hang it from my brake lever.

I cut the lines equal length with enough slack to easily get to the fwd/left carb. I use a box end wrench to adjust with the other end pinched between my thumb and finger. oposing thumbs are great aren't they?!

The oil I use is a dark 2 cycle.

I used a small set of needle nose pliers to stretch open the end of the tubing so that it fits over the vacuum port.

For the fuel valve I use a large syringe with a plastic tip on it. pull it gently with your ear against the tank and you'll hear it open. I also did this when I was draining the bowls and got a good flush out of them.
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