Why are carb vacuum lines "open"?

[OzJavelin]

On my '78 GS750 I went to re-install the fuel tank after painting it (started a long time ago), and noticed that what I would have thought were vacuum lines from the carbs (one goes to the petcock) appear to be vented to the atmosphere? On slide carbs, why aren't these blocked off like on CV carbs? And why are only three of the four carbs fitted with these ports? Confused ..

[Steve]

Two of those three lines are actually VENT lines, not VACUUM lines.

It has been a while since I played with VM carbs, but I think the hoses on #2 and #4 carbs are the vents, the one on #3 is the vacuum line to the petcock.

The vent lines should be routed up, over the airbox, into calm air. If the airbox has been removed and pod filters installed, remove the vent lines.

.

[OzJavelin]

Two of those three lines are actually VENT lines, not VACUUM lines.

It has been a while since I played with VM carbs, but I think the hoses on #2 and #4 carbs are the vents, the one on #3 is the vacuum line to the petcock.

The vent lines should be routed up, over the airbox, into calm air. If the airbox has been removed and pod filters installed, remove the vent lines.

.

Thanks. Explains a lot, but weird that they appear to be ported at exactly the same spot on the carb body?

[tkent02]

The passages in the carb bodies are drilled differently inside.