Vacuum for petcock

I have a 1979 kz650 b3 and I am wondering which vacuum nipple, of the three on carb number 2, I should use for the fuel petcock.
thanks,
Joe

I think it’s typically number 3.

 

So the picture shows that the nipples on 2 and 4 are vents, while that nipple on 3 is vacuum. I have that nipple on 2 and 4 blocked. Should I uncap those so they can vent?
thanks again,
Joe

They should be unblocked.  Normally there is a short hose attached to them to prevent spillage.

The carburetors in pic aren't VM24s (maybe VM26?), so they may be slightly different. You mentioned 3 nipples on #2. Got a pic?
Vent tubing helps to keep water out of the carburetors. The vent tubes on my 81 KZ650-CSR are routed over the airbox shoulders & downward then fitted snug between the airbox & side covers. The LH tube has a frame clamp. Yours may be done differently.  

Below is a pic of VM24s, purported to be from a 1979 KZ650 but not certain.
The vacuum nipple for the petcock is forward of the vent port (nearer to the engine side). It's hidden in this pic as it's lower than the vent.  There isn't a vacuum port on any of the other carburetors. Instead, the vac ports would have been on each of the carb holders on the cylinder head.  Only two of the carburetors have vent ports (#2 & #4) but the other two are vented via rubber connectors between the carbs. #2 vents carbs 1-2. #4 vents carbs 3-4. 



ps: I think the pic linked by mykaw might be mislabeled regarding the "vacuum fitting" on the #3 carburetor. that's probably a vent, but I could be wrong. a rubber vent connector between carbs 3-4 usually obviates the need for an extra vent tube. same goes for the other side.

The diagram at Kawasaki shows only one vacuum port. It is in carburetor number two very close to the flange that bolts to the carb holder. You can see it just below the 42 reference number. Carburetors two and four have vent tubes that are closer to the air box side and point away from the engine at about 45 degrees. 
You can also see the vent connector tubes Martin mentioned. They are reference number 39.
The nipples on the very bottom of each carburetor is for float bowl overflow.

www.kawasaki.com/en-us/owner-center/part...Z650-B3-_-PARTBUCKET

Vent tube routing. The 650B should have a baffle plate forward of the airbox, probably bolted to the frame. I think the vent tubes are fitted thru the sides of the plate & routed into the airbox.  This would ensure that the engine will burn any gasoline fumes for smog reduction. Some guys toss the plate or it goes missing. Lacking the plate, they probably route the tubing behind the engine. 

This may help. earlier carbs with no Accelerator pump on the bottom.

All of the vm24 or vm22 carbs that came stock on 650s that have a vacuum petcock have a port on carb #2 (left to right as you sit on the bike) that is just behind (towards the engine) the vent port .