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If you are talking about the hose being touched in the first picture, it doesn't appear to be connected to the carb at all in your pictures, or anything at all for that matter.

Could be a breather line from the crankcase breather to the air box? Such a hose can do its job with no clamps.

Your situation demonstrates why it's important to document in DETAIL. I used to draw little pictures and stick them in the ziplock bags with the parts, but now I take lots of digital pictures as I disassemble. They just sit on a thumbnail drive to get deleted later, but sometimes are very valuable.

The latest and greatest method is to have a couple of video cameras pointed at the task at hand. Then you can play back the video later and see just what you did when you were thinking about something else. There's always that one part that comes out attached to something else, drops off quietly when you aren't looking, and rolls away.
 

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Manifold vacuum port
Vacuum sources for California emissions evap diaphragm valves , I see photos of the carb body in the Service manual both with and without that hose fitting.
IIRC that is the same place the air-cut valve gets vacuum in the carb body.
If it isn't a California emissions bike I'd just cap the fittings and call it good.
Good call gentlemen!

Here's a write-up of somebody who wanted to remove the CA emissions stuff from their '98 750 ACE. California Emissions Removal – VT750DC.com There's a little discussion and some diagrams there. Honda calls the vacuum hose that powers the valve, #10, and it doesn't show if it is sourced from one carb or teed to both. My first instinct would be that crossing over the intake ends of the carbs of dual carbs would be a bad thing. Only one carb is sucking at a time, wouldn't mixture be motivated to go first one way, then the other through a crossover hose?

Unfortunately the image at the link that shows which ports the author capped is missing.

My VLX 600 is a CA bike, and I think that there is a fault in the vent emissions collection system that is causing the bike to run rich, but I'll investigate that further when I get some spare time to pull the tank and fool with it. I can look at how my 600 is plumbed at that time.
 
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So the gas tank and the carbs are vented into the charcoal canister, that stores the fumes, and then when the engine is running, valves open to draw the fumes back into the intake to be burned off.
It is OUTSIDE all the engine mixtures systems.
It appears to me that if the control valve diaphram is damaged, the intake manifold vacuum line could be sucking from the bowl vent line. With the vibration inherent in a moto, I would think this would include some amount of raw fuel as well as vapor direct to the intake port.

Other failure modes could have this same intake port sucking from the tank vent line, or sucking direct from the atmosphere if the purge valve is defective. I would think any of these faults would affect mixture, same as running with the choke on, or with a vacuum leak.

I'll investigate more and report once I get to the bottom of the issue. All I'm sure of at this point is that after clearing the usual suspects, and re-jetting to stock, my CA VLX continues to run noticeably rich and fuel economy is bad, high 30s for a machine that should be yielding almost 50 mpg.
 
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