TOPIC:

pa317 wrote: Darn! Now I have to track down an O ring for that (and probably the other three drain screws)

Alas, it took a whole 5 seconds to find several ebay listings by searching the part number. And a Google search produces not quite a zillion more sources.

Good Fortune!

I removed the gas tank just now. Fuel is freely flowing from the vacuum (#5 in the photo). I disconnected the hose from 7 first and no fuel was lost. Then disconnecting the hose from 5 and poof, it's all coming. It's going into a 5 gallon bucket right now.
1 - that's not supposed to happen, right?
2- other than buying a whole new petcock assembly, how can I fix this?
3 - Is it worth fixing this and trying it out without cleaning the carbs? Or do I start that adventure too?

No fuel should ever flow through the vacuum port. This must be at least the 50th time I've read about this problem happening with vacuum operated petcocks; I believe it is a sign that the diaphragm has failed.

You can try rebuilding it if you can find the correct kit; apparently there are a couple different flavors and if the wrong one is used the problem persists. Another option is to replace the petcock. I've owned bikes for 50 years; never had a vacuum operated petcock; and never found it a hardship to simply turn off the petcock when I turn off the ignition key, so If it was mine I would replace the petcock with a non-vacuum type and put a cap on the #2 carb vacuum port, but I'm sure others will disagree.
Ed

The good news is there is a rebuild kit for a kz650b. The items in the kit match up with the item numbers for a kz650c. $30ish bucks later, and it's in progress. I hope this will resolve my issues. Since the tank is off and I have the Golan fuel filter, that will get installed. At this point, I am not inclined to take the carbs out and clean them.

So is a vacuum operated function for convenience? Saves customers from having the step of turning fuel off each time ignition is turned off?

Yes, that's the only reason for the vacuum operated petcock. Ed

well that's dumb! If the rebuild kit doesn't solve this problem, I'll look for a different petcock that fits the tank. Would that petcock still have the on, res, and pri positions in addition to 'off'?

No, it will have OFF, ON, RES positions. There is no need for PRI since fuel will flow in ON and RES even if the engine is off. Oh, it may be marked RUN instead of ON.

That makes sense. I'll update this next week once the part comes in and let you all know how it went. My goal is to have this ready to go for a ride Friday morning

Here's what the petcock used on the 1977 KZ650-C1 and B1 models looks like. It is marked RES / OFF / ON. Ed

So that is what part 10 looks like from the diagram below. I wonder if the dimensions on how it works with the tank are the same as the vacuum controlled one.
www.kawasaki.com/Parts/PartsDiagram/144023/1979/KZ650-B3

Here's the hole spacing.....