79 KZ650 Carb Overflow and Petcock issues

I've recently developed an issue with the #1 carb overflowing out of the vent tube. It pees out gas until it gets down to the reserve level, even when not running.

Also, my petcock doesn't seem to be vacuum operated anymore. It's constantly flowing. Even after replacing the diaphragm with a kit from Z1.

Do you think the overflow is related to the petcock issue, floats or both?

Any assistance would be great.

Hi TPOL,
First welcome to the KZR Nation it`s really great to have you here.

IMHO and as you have guessed already, you have two separate symptoms. First, the No. 1 Carb is overflowing because the Fuel Service Level is too high in the float bowl.



This could be caused by one or both floats being flooded. However, it much more often caused by the Needle Valve not shutting of completely. This could be due to a deteriorated Needle Valve Seat to Needle Valve matting. The solution is a new (not expensive) replacement see our friends at Z1 Ent.

Still more common is dirt or debris lodged between the seat and the needle. The cause here is a dirty tank. The solution is to clean the tank, install a good quality, clear, inline fuel filter (not expensive) between the Petcock and the carbs and to clean out the carb. Again, I get mine from Z1.

In all cases you will want to do the Fuel Service Level
adjustment as per your FSM.

Second you have a free flowing Vacuum Operated Petcock. I have never worked with one so I prefer not to comment and to await input from more informed sources. However, I suspect you solution may lie in cleaning out your petcock or changing out for a Manually Operated Petcock. Z1 can help. I understand a Suzuki Petcock of the same vintage is available as a bolt in swap at an affordable price. I went for the Pringle after market Petcock which has worked fine but I`m not crazy about the routing of the gas line out the side rather than out the rear as in the OEM model.

Best of success.

PS,
Don`t forget to add your year, model and location to get the best responses... and it`s considered real friendly too.
Bill

Thanks for the welcome and all the information. I have a 1979 KZ650 SR. We hadn't had any problems with the carbs overflowing before, even with the free flowing petcock but the tank did have to be cleaned. I suppose something got lodged in before we cleaned and reinstalled the tank and it is holding the float open. Time for another carb pull.

Yea, you have 2 problems. A good set of carbs will not leak even if the petcock is stuck on. The vacuum petcock diaphram is a delicate thing. All needs to be assembled just perfect or it won't work. Use Kawasaki parts, cheap at $12 or so for the petcock kit and works. Other brands may or may not work is why I stay Kawasaki.

If no issue found with float valve or float or float setting, would also check for a crack in the overflow tube (#6 in the above posted diagram).

Good Luck!

The vacuum petcocks are afflicted by essentially the same problems as the needle valves - deterioration and crud. The solutions are also basically the same - clean the tank and clean and rebuild the petcock. Also as mentioned above, the factory replacement parts are not terribly expensive and the job is quite easy, but care is essential, especially with the diaphragm as it is very thin and easy to damage.