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Author Topic: carb vacuum port question cb750k1  (Read 3113 times)

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newcbguy

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carb vacuum port question cb750k1
« on: January 09, 2008, 10:01:15 AM »
I have 2 ports between carb 2,3 which appear to be vacuum port hose connections. Where do these connect to? should I connect them together? I am running pods. In the parts fische it shows 2 hoses coming off of them but doesnt show where they connect to. I currently dont have them hooked to anything.

thanks
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Offline Jonesy

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Re: carb vacuum port question cb750k1
« Reply #1 on: January 09, 2008, 12:25:04 PM »
They hook to the open air... :D

Seriously, they are bowl vent hoses. They keep the carb bowls vented to atmospheric pressure. Your vacuum ports are capped with brass slotted screws, one on each carburetor, next to the intake rubber connectors going to the cylinder head.
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newcbguy

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Re: carb vacuum port question cb750k1
« Reply #2 on: January 09, 2008, 01:45:40 PM »
ok so they aren't vacuum ports, thats good. I guess it doesn't matter to not even have a hose connected to them then?
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Offline dustyc

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Re: carb vacuum port question cb750k1
« Reply #3 on: January 09, 2008, 02:18:13 PM »
The tubes should end up down by the swingarm where your overflow tubes go.  I suppose there is a chance of gas coming out of them under certain circumstances, and you would rather have it on the ground than on your engine.
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Offline Bob Wessner

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Re: carb vacuum port question cb750k1
« Reply #4 on: January 09, 2008, 02:40:46 PM »
On mine, they are listed as 240mm, or about 9". I believe they just drape over the top of the airbox. As to whether you can just forget them, for many years I rode mine without them only because I didn't know they were supposed to be there. Only after looking at a manual and parts list did I realize otherwise.  I don't recall any issues not having them.

I guess I should add that Honda rarely wasted time/money on anything non-essential so I had to assume they had a reason for installing them. The only one that comes to mind is carrying vented fuel fumes to a safer location away from heat or other sources of possible ignition.
« Last Edit: January 09, 2008, 02:56:56 PM by Bob Wessner »
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Offline TwoTired

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Re: carb vacuum port question cb750k1
« Reply #5 on: January 09, 2008, 03:07:02 PM »
Vent tubes are hosed to limit water, dirt, and insect ingress, all of which can make the carbs problematic.

Cheers,
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Offline dustyc

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Re: carb vacuum port question cb750k1
« Reply #6 on: January 09, 2008, 03:25:41 PM »
I may be wrong about the 750 k1, that's where they are on my 500.
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Offline Clyde

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Re: carb vacuum port question cb750k1
« Reply #7 on: January 09, 2008, 05:28:56 PM »
On one of my manuals they show them going forward and up underneath the tank - alongside the main frame tube, and being held in place by a strap.
They are about 9 inches long.
Regds Clyde
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Offline Bob Wessner

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Re: carb vacuum port question cb750k1
« Reply #8 on: January 09, 2008, 06:59:24 PM »
Quote from: Clyde on January 09, 2008, 05:28:56 PM
On one of my manuals they show them going forward and up underneath the tank - alongside the main frame tube, and being held in place by a strap.
They are about 9 inches long.
Regds Clyde

Interesting, thanks.
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newcbguy

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Re: carb vacuum port question cb750k1
« Reply #9 on: January 09, 2008, 07:00:32 PM »
thanks for the info guys
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Offline Head

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Re: carb vacuum port question cb750k1
« Reply #10 on: February 14, 2008, 08:25:48 PM »
The vents have the tubes on them to prevent any fuel dripping out on splashing or what ever you want to call it.74 and up have a white clip on them. Head
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kta

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Re: carb vacuum port question cb750k1
« Reply #11 on: February 14, 2008, 09:19:43 PM »
The tubes typically come up over the carbs and route around the airbox to drain by the swingarm. I always just take mine off though. If your carbs are in good shape there shouldn't be much of a risk of gas coming out from there, and if gas was coming out of those ports your bike would be bogging very badly and you'd know there was a problem right away.
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