RPMs shooting up - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 7 (permalink) Old 06-30-2015, 01:24 PM Thread Starter
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RPMs shooting up

She starts up fine and idles nicely. The problem is that once I lay on any amount of throttle the RPMs shoot up to between 5 and 7 thousand, and stay up there even when I let off the gas

My throttle cables and throttle mechanics on the carbs all work fine, opening and closing in accordance with the throttle itself.
The only explanation I could think of, is that there is a vacuum leak somewhere.

So I ran with this theory, i've had my carbs in and out a couple times, so I guessed the chances of me making a leak someplace were likely, and potential holes could be anywhere on the boots, the surge tank or the connections from the surge tank to the carbs.

I gave her an earshave, because I'd wanted to anyways for one, but mostly because as far as I could tell, the earshave procedure would cross off any possible vacuum leaks except for the boots themselves.
In the process of the earshave I removed the carbs and examined the boots, they looked fine, then I took great care to put them back on the correct way.

Well I just finished the earshave this morning and started her up and I still have the exact same problem.

Any advice?
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post #2 of 7 (permalink) Old 06-30-2015, 01:37 PM
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Are you absolutely sure the boots are one correctly with the little tabs matching up to the bumps on the intake?

On the right one you can see the little tab. there is a bump on the head that this matches up to.


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post #3 of 7 (permalink) Old 06-30-2015, 01:51 PM Thread Starter
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Only one of my boots has the nipple, but between observing how that one connected to the cylinder and seeing where i was pretty sure the nipple used to be, I'm nearly 100% positive they are correct.
That's why I'm so confused.
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post #4 of 7 (permalink) Old 06-30-2015, 02:48 PM
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There is a bolt at the bottom of the two carbs that is upside down. When the carbs rev up, turn that screw in either direction, REMEMBERING how much you turned it (quarter turn or half) so you can return it to it's position and does that make a difference? Just wondering if your butterfly valves are stickin

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post #5 of 7 (permalink) Old 06-30-2015, 05:13 PM Thread Starter
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If my buttefly valves were sticking open wouldn't I have been able to tell while my carbs were off? everything slipped easily open and closed last night when I had them off, any reason why it would be different once they're on?
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post #6 of 7 (permalink) Old 07-01-2015, 01:48 PM
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check to ensure your "choke" mechanism is free and not stuck in the "out" position. The slider on the carb might also be leaking.
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post #7 of 7 (permalink) Old 08-30-2015, 03:28 PM Thread Starter
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I think the vaccuum leak was coming from a replacement spark plug the previous owner put on that didn't quite match the other 3 and was a little loose. The problem is fixed now!

Thanks everyone for your help!
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