Air noise from carb intake when idling - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 6 (permalink) Old 01-28-2020, 11:20 AM Thread Starter
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Air noise from carb intake when idling

I just recently disassembled my '86 carbs and clean w/ carb cleaner. What i've notice though, is there is a vacuum "sucking" noise from the carbs while running at idle, especially with the choke on. Is this normal? Or could I have a vacuum leak from one of the carb boots or elsewhere?

Thanks guys.
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post #2 of 6 (permalink) Old 01-28-2020, 01:47 PM
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I just recently disassembled my '86 carbs and clean w/ carb cleaner. What i've notice though, is there is a vacuum "sucking" noise from the carbs while running at idle, especially with the choke on. Is this normal? Or could I have a vacuum leak from one of the carb boots or elsewhere?

Thanks guys.
I notice a similar noise with the choke on, too. It lessens a bit when I cut the choke off, but the carbs ARE literally sucking air into the engine, so I'd say it's probably to be expected and normal so long as the bike is running properly

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post #3 of 6 (permalink) Old 01-28-2020, 06:41 PM Thread Starter
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Great to know I'm not alone there. I've had the pod air filters off running it too...maybe that is making the noise apparent. Thanks!

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Originally Posted by jakob_rothfuss View Post
I just recently disassembled my '86 carbs and clean w/ carb cleaner. What i've notice though, is there is a vacuum "sucking" noise from the carbs while running at idle, especially with the choke on. Is this normal? Or could I have a vacuum leak from one of the carb boots or elsewhere?

Thanks guys.
I notice a similar noise with the choke on, too. It lessens a bit when I cut the choke off, but the carbs ARE literally sucking air into the engine, so I'd say it's probably to be expected and normal so long as the bike is running properly
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post #4 of 6 (permalink) Old 01-28-2020, 07:51 PM
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If you had a vacuum leak it would probably make the idle erratic because the mixture would get thrown off. I’m far from an expert but I don’t think it’s a good idea to run the engine with no air filters, you run the risk of sucking dirt into the engine.
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post #5 of 6 (permalink) Old 01-28-2020, 09:30 PM Thread Starter
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Absolutely agree with you. I was just still in the testing phase and had the bike in the garage on the centerstand. Yeah, the idle is pretty smooth, aside from a spike in RPMs when the motor is cold and the choke is close completely.

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If you had a vacuum leak it would probably make the idle erratic because the mixture would get thrown off. I’m far from an expert but I don’t think it’s a good idea to run the engine with no air filters, you run the risk of sucking dirt into the engine.
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post #6 of 6 (permalink) Old 01-29-2020, 10:49 AM
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These carbs really sound off loudly with pod filters. With pods removed, ports at the carb intake are exposed, which affects performance, and you'll also hear a lot of extra air. Sometimes you can hear the fuel flowing, a sort of spitting sound.

It's normal for rpm to rise with the choke in use, and as it warms up, rpm will continue to rise if the choke setting isn't reduced.

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