TOPIC:

Hey guys,
Long story short, I picked up my first bike last a summer - a project 1981 KZ650 CSR. Still working on trying to get it to start but no luck....yet. You may hear more from me in my endeavour!

Quick question - on the engine side of the carbs, I see rubber plugs on three of the carb holders but a line coming off of carb #3. For reference, in the 1981 KZ650 manual, I'm looking at part #47 on page 6-18.
Should each carb holder have a plug or does that line need to be there?

Thanks guys!

It's a vacuum line to make the petcock function.  It may also branch off for the air injection system, not sure since I don't have the manual you reference.

Are you sure there's tubing from a carb holder to the #3 carburetor?  I'm assuming that's what you mean.
Sounds like someone connected a carb holder vac port to a carb vac port. 
Does the motorcycle have a vacuum petcock or manual fuel valve?
just in case:  the carburetors are numbered 1-2-3-4 L-to-R as you're sitting on the motorcycle.

I have the same motorcycle. Stock, there's a vacuum port on the #2 carburetor w tubing connecting it to the petcock on the fuel tank.  The #2 & #3 carb holder vac ports are capped w rubber plugs.  The #1 & #4 carb holder vac ports have tubing connected to the Kawasaki clean air system.  Additionally, the #2 & #4 carburetors have vent ports which should have tubing routed over the airbox shoulders & open to atmosphere.


 

It's a vacuum petcock. I have the two lines going to the petcock (fuel + vacuum). And yes, I have the two vacuum lines coming from the carb back up over the airbox.

It's on the other side of the carb that I am looking. I attached the page and the plug that I'm looking at (part #47). 
Should there be four plugs on each holder?

Thanks for your help, guys. Really appreciate it.

If there's a vac line from the #2 carburetor to the petcock and the Kawasaki clean air system is disconnected,
then I would say yes, all 4 should be plugged.  Stock two vac ports are plugged.  If the Kawasaki clean air system is removed, then all 4. 
You may need to post a pic of two of your carburetors.  I already looked at that image from the manual.  

In the topic post you say three carb holder vac ports are capped & you have a line coming off carb #3. 
Where does the other end of that tubing connect?  and are you sure it's carb #3? see 1-2-3-4 L-R stuff above.

ps:  the two lines over the airbox shoulders are vents (not vacuum).

What do you mean "Kawasaki clean air system"? 

Yes there is the vacuum line from carb 2 to the petcock.

I snapped a pic of the line and the caps that I am talking about. I could not find anything in the service manual about quantity of caps. What is the purpose of those caps? I am assuming it is for diagnostic purposes.

And yes, I am positive it is carb 3 (I'm a parts manager in a Dodge/RAM/Jeep dealership - I learned early on what is 'left' and 'right' when talking about parts!) Appreciate the simple question, though (aka 'have you tried turning it off and back on again?!').

Thank you for correcting me on vacuum lines vs vent lines. Yes, I mean vent lines.

The tubing in the center of your photo is connected to the #3 carb holder vac port.  Where does the other end connect?
The caps are for the carb holder vacuum ports.  If left uncapped, you'll have a big vacuum leak & the motorcycle won't run right (or not at all).
The vac ports are used to synchronize the carburetors >> the plugs are removed & a synchronizer tool connected.

The clean air system is the smog assy connecting the valve cover to the airbox. Some guys get rid of it.  It's kind of a passive method of introducing fresh air into the exhaust system to help burn off any unburned fuel & other emissions.  When eliminated, you have to cap the vacuum ports, plug the airbox port & plug the valve cover ports.   
In the partzilla link click the Air Cleaner diagram & the Cylinder Head Cover diagram. 
The large clean air system tubing connects to the valve cover ports & to the airbox.
www.partzilla.com/catalog/kawasaki/motorcycle/1981/csr-kz650-h1

 

The other end of the hose connects to nothing! 

And since I have had the bike (with this mysterious hose attached), I have never been able to start the bike.

Could this hose be the answer to all of my life's questions?!

Thanks so much for your help!! 

Ha ha.  Use a good automotive rubber plug to cap it.

Do you have the clean air stuff?  I'll guess no since the #4 carb holder is capped.

ps:  in your pic the tubing is connected to the #3 carb HOLDER (not the #3 carb).

I looked at the Partzilla link that you sent and to the best of my knowledge, no, I do not have that clean air system with my bike. 

Again, super appreciative of the help! I'm excited to get home and see if I can finally get the bike started. The benefits of working in a parts department is that I'm surrounded by automotive grade stuff all the time (hence why I took on this project in the first place). 

Is the airbox still installed?  That would be a good thing.