Vacuum actuated petcock does not stop fuel.

I recently repaired the vacuum actuated petcock on my newly acquired KZ650 SR. It was leaking fairly badly when I bought the bike. I went to the local dealer, gave him my VIN, looked at the pics and thought we figured out which parts I needed. I took the petcock apart, cleaned it thoroughly, and went to put it back together. All of the o-rings matched, but the vacuum diaphragm and associated seal were different. The original spacer was a bit thicker, and had a boot type seal on the fuel side that sealed both the mating surface between the petcock and spacer as well as the fuel stop. The new one was a bit thinner, used a very thin gasket on both sides, and only had an o-ring for the fuel stop. Anyway…

When I put everything back together and started putting fuel in the tank it spewed from between the petcock body and the vacuum assembly.

I disassembled the petcock and installed the boot over the new vacuum assembly, over the o-ring and reinstalled. No leaks!!!!

A few days later I went to remove the tank to work on an electrical problem, and found that the petcock does not stop the fuel.

Now the questions: Will this cause me any problems in the future? If so, what are they? Where can I get the right vacuum assembly (dealer has no clue)?

Thanks for your help.

Petcocks are a pain in the A$$. I've given up rebuilding them. Generally the filter screen is shot any way. I've always been able to purchase a whole petcock.

To answer your question: Yes it's important that the petcock function correctly. If the petcock allows the fuel to continue running It's possible to fill the crankcase with a gas/oil mixture, or even worse, it's possible to hydraulically lock a cylinder when you hit the starter.

KZCSI

Post edited by: KZCSI, at: 2007/04/26 13:32

Seems that the odds on rebuilding petcocks are generally in favor of starting out with one that ain't whooped to begin with. Don't know the exact shape yours is in, so it's hard to say.

A common source of seepage with these birds is a lack of tension on the shutoff spring (#92081 in the pic below). When the motor shuts down and the carb vent quits drawing on the diaphram, the spring presses the diaphram closed and shuts off flow. At least that's how it's supposed to work anyway.

Might be worth pulling it apart again and giving that spring a bit of a stretch - they tend to weaken over time and don't put out quite as much as they did when they were younger.

My problem rests with part number 43028 and o-ring 670. The original vacuum diaphragm did not look exactly like 43028, and did not have the o-ring 670. Instead it had a neoprene boot that covered the shaft that o-ring 670 fist on, and sealed both the vacuum diaphragm assembly to the petcock body and the fuel inlet when there was no vacuum.

When I tried the dealer supplied parts (as seen in your diagram) fuel spewed everywhere, no seal at all between the diaphragm assembly to the petcock body. I added the boot over the dealer part and no exterior leak, but it does not seal internally.

Now the question is where can I get a diaphragm assembly with such a boot? The dealer is lost.

Post edited by: Willie, at: 2007/04/26 14:43

Post edited by: Willie, at: 2007/04/26 14:47

Willie wrote:

My problem rests with part number 43028 and o-ring 670. The original vacuum diaphragm did not look exactly like 43028, and did not have the o-ring 670. Instead it had a neoprene boot that covered the shaft that o-ring 670 fist on, and sealed both the vacuum diaphragm assembly to the petcock body and the fuel inlet when there was no vacuum.

Ah. My bad - I just had the drawing for the KZ1000 petcock lying around and went on the assumption that they'd be similar critters.

Similar, but not similar enough. :blush:

Now the question is where can I get such a thing?

Don't rightly know offhand, but there's some pretty fair 650 hands around that are sure to have better ideas than mine...

The KZ650D1 diagram is the same. The dealer and I spent at least an hour looking at various models for the same part as was originaly there. All have about the same setup, shaft with an o-ring.

Ah. Not the first time I've run into undocumented mods myself.

Me being what I am - generally a seeker of the path of least resistance, I'd suggest picking up one of those "other models" somewhere if the mount's the same.

There's probably at least a dozen people around here that'll home in on this thread that have one lying around in workable/rebuildable shape that'll make you a deal on it.

If it fits into your budget for your bike (about $90), just buy a new petcock and be done with it.

It sure beats the frustration and aggravation of "Mickey Mousing" it and finding out that it only partially works, or created a leak elsewhere as you're experiencing

There's a couple of petcocks available at Z1. One's an aftermarket with adapter for about $90. Anothers a Suzuki OEM unit for about half that.
Mine's an El Cheapo Briggs+Stratton lawnmower type that I put in my gas line after my petcock. It works great, just gotta remember to turn it off. It was about $7.

There is a gremlin inside the tank which blows fule out the vent hose next to the negative battery terminal on my Vulcan 1500 C3...after winter storage.

Had image of being hit by a Tiger Tank with one back-fire.

What can cause this raw gasolene gush?
- Stuck float in tank due to emptying it for winter storage?

- The turn off valve over engeneered?

- ule tank needle valve out of seat inside the tank?

- Free-flow from a bad design in 1996 which should have been a recall?
One of the carbs needle valves stuck open with varnish?

Or !

Tanked Leprecaughns vacationed in the tank, so I should just drink the Potsheen and shut-up...but dont start her up and spoil their fun?

Jack O'Brien

If no help my friends, then it's up to the shop with $500.00 so there goes the Nova Scotia ride this summer. Mercy me

fathom, since you're asking about a Vulcan, might I kindly suggest a forum with more Vulcan riders? Kawasaki Motorcycle Forums is a good one for your Vulcan questions.

Willie, a relatively simple fix is to go with a manual fuel tap. Z1 Enterprises has a Pingle adaptor plate (44 mm bolt spacing on my SR) that will allow you to install a fuel tap with 3/8" NPT thread. They also offer a generic manual manual petcock that is about 15 bucks.

For about $30 you can forget about the vacuum job. Most likely, once you kit it and get that part to work properly, it will do as both of mine did and start leaking where the elbow comes out of the petcock body.

With the manual tap, you're in control of the fuel flow, so you need to remember to turn it on!

Well, it has been about a month since I last worked on the petcock problem (spending my time on other parts). The vacuum actuator is still not sealing the fuel completely off, but the bike continues to run. The bike has about 480 miles on it with this problem with no apparent ill effects.

It is starting to have either timing chain or cam chain tensioner problems. It is rough at idle, but when you give it a bit of throttle it smoothes out. I replaced the plugs, wires are in excellent condition, replaced the points (whole plate), and adjusted the timing. When I put a timing light on it you can see the mark position is unstable at idle. If you give it just a little throttle the line stabilizes nicely. I have set, checked, reset, and rechecked the points gap and timing adjustment.

I got tired of working on the thing so… I bought a 2006 Vulcan 900 and have been smiling ever since!!! My Father-in-law has been riding the KZ back and forth to work and around town. It continues to run well.

I have had time to ride both bikes back to back, and the KZ definitely has its high points. It is just as quick, good power to weight ratio, has better handling, and seems to be more stable on uneven surfaces and in windy conditions. The problems with the KZ are: the bike is not comfortable over about 65mph (it seems to be working really hard), and I have to work on it all the time.

We will probably just ride it until something goes wrong that can’t be easily fixed.

Ride it until it dies!!!:evil: