Gas in my vent lines - 1976 KZ400 D3

I never had these lines actually hooked up to the vent tubes until recently, so I guess that's why I never noticed this. But the other day I looked down and noticed a bit of gas in my clear vent line that comes out the side of the #1 carb. My bike also runs rich - so much so that if you put the choke on at idle it will stumble and eventually die. I have stock jetting, stock air box, new emgo air filter, stock exhaust w/ baffles. Could it be that my floats are set too high, and that is causing both the rich condition and the small bit of gas to drain down the vent line when the bike is parked on its side stand?

When I first noticed the gas in the line, I had had the carbs off the bike. They were reinstalled but I didn't fire it up until the next morning and that's when I saw it... If that matters.

It sounds feasible. Would recommend the clear tube test to check float fuel levels. Can be performed with everything on bike, so it's a good/easy place to start. If your float levels are real high, it's possible that when you go to the sidestand, you're getting some fuel sloshed into the vent line.

That's what I'm thinking. Would a float level that's too high also cause it to run rich?

A too high fuel level will cause an excessively rich mixture in an otherwise perfect carb.

The clear tube tests shows the fuel level, which is the critical factor.

The "correct" float height is whatever happens to result in the fuel level being within spec.

When all fuel levels are within spec as determined by the clear tube test, the float heights may differ from one another among the carbs.

As known, a hose runs from a carb vacuum nipple which supplies vacuum to a vacuum operated petcock.
A defective diaphragm in a vacuum operated petcock may allow gasoline to exit the petcock by entering into the vacuum tube and flowing down to be sucked into the air/fuel mixture being supplied by the carb.
Which enrichens the mixture being sucked into the combustion chamber.

Am thinking that the fuel level inside the float bowl must be abnormally high in order to flow into a vent opening.

Good Fortune!

All else normal, a high fuel level in the carbs will cause rich condition