Fuel Overflow On My stock 77 KZ650 B1

Some petcocks have a small spring to hold a plastic cone snugly in its position inside the petcock.

It's easy to lose the spring, or simply forget about it.

When reassembling the petcock, be sure to include the small spring.

Without the spring, the cone won't fit snugly, and some fuel will leak around the cone instead of all fuel flow being contained within the hole through the cone.




As I recall, it's also possible to erroneously insert the cone 180° off.

Good Fortune!

Yea check for the spring. Otherwise there is no magic to this petcock, If you get tired of the manual piece of utter crap, any similar era vacuum petcock with the same mount bolts right up. You can use a 78 up KZ650 vacuum petcock and just run the vacuum line down to one of your sync nipples on any of the 4 intake manifolds. There is still something wrong though, because on a properly set and working set of carbs gas will never leak even if the petcock is left on.

Fuel discharge from the carb overflow often results from an imperfect float valve, perhaps from dirt or grit preventing a perfect interface between the pointed tip of the float needle and the orifice in the float needle seat.

Various methods may be employed toward removing any such crud from the interface.
• SeaFoam added to fuel in the tank;
• Rapping smartly against the float bowl with a plastic mallet while the engine is at idle rpm;
• Flushing -- by allowing fuel to flow through with the drain open;
• Disassembly and cleaning the needle and orifice (and perhaps using a q-tip chucked in a drill).

Or the float needle may be worn out, perhaps evidenced by a groove in the pointed end where it fits into the seat orifice.

A leaking or sunk float may also fail to close the float valve.

And a hanging or sticking float may also fail to close the float valve.

A float installed upside-down will fail to close the float valve.

Another possible cause for fuel discharge from the carb overflow could be a cracked or loose overflow tube (inside the float bowl), which is often repairable.

The float tang adjustment -- which sets float height to achieve correct fuel level -- usually isn't reponsible for fuel discharging out the overflow. Because a correct tang setting does not spontaneouly get out of whack incident to normal use and riding of the motorcycle.

Good Fortune!

Thank You Gentlemen! Thank You! Patton, more great info! Ron and Ed, also great stuff. I knew that I should have checked back here first but in the meantime: I placed an order from Z-1 Enterprises for a Vacuum Petcock, $64.40 including shipping. This looks slightly better than the current EBay bid on the gravity fed one just like my original. I wonder if I lost that spring when I last put the petcock back together. I will have to disassemble to find out. Who knows, I may have a working petcock and don't even know it. :pinch: Maybe get a spring at Ace Hardware? Again, thanks to all of you for some absolutely awesome info and pics. Will post the final outcome in hopes others do not need to go through this experience.

floats offset?

Didn't mean to ignore this thread. Thanks again to everyone for your interest and feedback. I don't think the floats sticking or offset is the problem. I do know that since putting the Z1 Enterprise supplied Suzuki vacuum petcock, I have experienced irregular fueling. I got the bike running put more fuel in at gas station and then went out on my favorite stretch of open road. I opend the KZ up to 90-100mph and then the bike behaved as though I had run out of gas. I sat there on the side of the road fussing with the fuel line, kink? and such. Waited, then bike fired right back up. I rode home at a more relaxed pace. Now the real kicker is I have not been able to start the bike since. It acts as though fuel is not being delivered. I wonder if I have not got the proper vacuum line set up. I did test the lines and do have vacuum. Not sure of the problem. I just wish I would NEVER have lost the original petcock spring that kept the cone in the sealed position. See Patton's diagram. I need a spring! or need to get this vacuum petcock to work! Otherwise this ole KZ is flawless! Thoughts/ideas are welcome.

so there is fuel coming out of the bottom of the carbs, my best guess- and I have been wrong on my guesses in the past- I think maybe the o-ring on the screw on the bottom of the float bowl may be bad, the float bowl itself may be cracked. this causing the fuel to exit the carburetor before it fills up again. so the problem you are dealing with is more in the carburetors than the fuel supply.

I will check it out Don. Glad you noticed the posting since you were last to reply a few months back. Thank you!

Epilogue Update:
- Went from fuel leaking past the petcock causing fuel overflow issues.
- Small spring in the stock fuel petcock lost during disassembly or reassembly, causing the fuel to leak past petcock via gravity.
- Installed new fuel petcock, vacuum type, now fuel not reaching the carbs and intake. Kinked vacuum line the culprit. Also went from single carb vacuum to a dual carb vacuum via a T connector for the vacuum line of the fuel petcock.
-Still had starting issues. Discovered the battery had gone through so many charging cycles that almost all the water in the cells had been cooked off. I replenished the depleted battery cells AND YES! Bike starts and fuels just fine. The battery had been clouding the fueling issue but I did learn the vacuum line can kink. The aftermarket vacuum petcock is really made for vintage Suzukis and there is a tight fit in relation to the vacuum connection. Actually both the vacuum and fuel connector point rearwards and almost into the frame.

Moral of the story: You can turn a simple problem or bike issue into a complex one if you do not check the basics such as battery level after long storage and fuel line/vacuum line kinks or restrictions. Thanks to everyone for sharing info. Rode the bike this weekend over 100 miles without any issues.

Vacuum petcocks are junk,always have been always will be.
Invented for lazy yuppies, if you can't turn the petcock off when you park, you have no business riding a bike :whistle:

Mine works fine

Never had any problem with mine.

Glad to hear the 650 is up and running.