The secret life of a petcock?

So I bought my ZX750A1 in the fall of -15 to have as my daily beater while I am doing the restromod on my Gpz750R1. But the bike was quickly renamed the Ebola bike as bodily fluids was poring through every opening and close enough through its bare skin. Last year’s multiple carb cleaning, tank cleaning and petcock rebuild was in vain as the bike topped of last year by draining 19liters of fuel through the crankcase.

While I was at it last year, I was surprised that after I had rebuild the petcock, it took quite some time for the petcock close after I had applied a bit of vacuum on the vacuum port of the petcock.

I guess that 1-1,5 dl continued to flow before it shut closed.

In order to get the Ebola bike in shape this season I tore down the head, slapped on a Athena cylinder head gasket. I know Nessism will curse me now for not using a Kawa gasket, but I will tear this engine down as soon as the Green Kwack is done, so I thought I could do in the meantime.

Cleaned the tank with hydrochloric and phosphoric acid this time and got it spanking clean and dried out before any surface rust formed.
Set the valves, cleaned that carbs yet again and to top it off, rebuild the petcock yet again (no worries Nessism, using only OEM parts this time and throwing away the aftermarket parts I fitted last year.

But while I was tinkering and cleaning the COVER ASSY,TAP as Kawasaki so poetically calls the part (16146-1005) The vacuum lid from where the vacuum tube to the carburetor goes, for us not so poetically inclined.

I noticed that when spraying carb cleaner through the lid it only passed from inside the chamber, not from the tube.

Could this be the reason the petcock doesn’t close? Or is it supposed to act as a check valve, which it pretty much does right now. The FSM states “The vacuum pulls the diaphragm against its spring pressure, and the O ring on the diaphragm assembly is pulled out of its seat, permitting fuel to flow between the O ring and the seat. When the engine stops and vacuum is lost, air enters the diaphragm vaccum chamber through the vacuum hose . . . . . . . . .”


Any how the only thing better than one Gpz750 is two, so I robbed the petcock from my other bike and it closes instantly when the vacuum is released.

I really want to understand what the case is here, and even though I was thinking about disassembling the working part to see if its open from both direction, but I chose not to, at least until I know how it is supposed to work.

Any thoughts?

Anders

As I understand, the check valve is there to prevent a backfire from reaching the petcock and rupturing the diaphragm.
The plastic insulator that the diaphragm mounts on has a lateral vent channel cast into it on one side. If the part is installed backwards, it may not be able to release the vacuum, thus creating the slow closing you describe.

Right Texas.
With a check valve in the fitting of the lid, and if air was able to enter through that little chanel the goes in the plastic part between the diaghram rubber it would all make sense.
Still it doesn't explain why mine is not shutting in good order. The compleete diaghram is brand new and I even replaced the return spring last year (yep oem spring)

/A

Hmmm, that is an odd one. Midget zombie apacolypse? Global warming?

Is it possible that something is causing the oring to hang up on the side of the seat as it closes? Maybe the post is off center or the oring is malformed. Yes, grasping here.....

Could that little check ball be hanging up in some way that slows the release of vacuum??

Did you inspect the o-ring mating surface on the petcock body? maybe it's pitted or scratched or something?
Mine was in good condition so I just polished it using brass wool. steel wool would work as well.
or do you mean the diaphragm isn't physically closing properly. if so, then never mind.

The plunger, oring an mating surfaces are top notch.
It has to do with the cutoff valve, I didn't take that apart, guess that it is made up of a steel ball and spring but wanted to get a better understanding before I dig in to it.
Tks Anders