Carb vacuum line?

[Northern Mike]

I'm having some issues keeping my GS750e (1979) running when not on prime. Even at speed (4k rpm) if I'm in the ON position, she starts to bog like she's starving. Did a quick Google check and found mention of the vacuum line being a possible issue.
Checked my bike and noticed in the center of the carbs a hose disconnected. All others go down and vent below the bike, but this one appears as it should have been connected to the petcock valve. Am I correct or out to lunch?
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[Big T]

The one that comes off the #3 carb, just to the right of center, is the vacuum line to the petcock

Hook it up and see if all of your issues go away

[Steve]

Yep, that's the one.

Connect that fitting to the smaller fitting on the petcock, you will be able to use the ON position, instead.

.

[Northern Mike]

Thanks guys. I figured that was the vacuum line connection and was looking for confirmation. The line that was disconnected (both ends) was for it, but is too big. Going to see if the truck stop down the hwy has something as its a stat holiday here, so nothing else is open.