It's Time for my Annual Petcock Diaphragm Change

I've been putting about 7,000 miles per year on my bike and about once per year the petcock starts leaking out the sides past the diaphragms. I order a new diaphragm, install it, and all is well for another year. The flange surfaces are flat and free of any scratches, pits, etc. The diaphragms are not getting holes in them. They are tissue paper thin and I would think that slightly thicker ones would stay sealed much better.

Has anybody had similar experiences, and is there a more permanent solution? Thanks.

That's strange. I'm still using some that may actually be original, or at least 10 years or more since I bought the bikes.

Have you been able to determine where they actually leak from?

I'll give my experience. 82 KZ1000, pretty sure the diaphragm was original, took a 3600mi trip. Added Sea Foam to tank 250mi from end of trip, diaphragm started leaking in 40mi or so. So coincidence, or just do to fail? I think from looking at it that is was from the additive. Which by the way didn't help, I found a small piece of air filter foam in a air bleed. Should have removed and washed that housing. Hind site = 20/20 every time.
But it will be quite awhile before I can say if the replacement, from Z1, will hold up.
So do you run an additive in the fuel?

I've read/heard that the E85 gas will eat the diaphrams and other rubber carb bits. I believe the #@$&%** in Washinton were too quick to pass legislation mixing gasoline with Alcohol without researching the affects.

You're on the right track with that, other than the E85, that's not supposed to be used in a standard engine. But the amount of Ethanol is supposed to be limited to a max of 10%. But some stations have been caught and fined with ratio's much higher.
The MTBE used and sold as Oxygenated fuel, was a real problem, it melted plastic in line filters, tore up in- tank rubber hoses, and dissolved some carb diaphragms.
Methyl Tert-Butyl Ether, nasty carcinogenic stuff.
Google has many articles on this stuff.
I remember a winter season in Fairbanks AK when this stuff was mandated by the EPA, we replaced a whole bunch of fuel system parts that year!

I have not been using any additives at all. I hear what you are saying about todays gasolines / alcohol, etc.

My petcock is vacuum operated. It actually has 2 diaphragms that form a sandwich about a plastic piece. Then the main housing and the outer aluminum flange complete the assembly. There is a small pressure relief hole that exits on one side of the assembly and THAT is where the leakage occurrs most often.

Once again, I am estimating that the diaphragms are not over .008" thick. There is very little to compress.

More ideas please?

Might be mistaken, but thinking fuel should not touch the diaphragm.

Vacuum overpowers the spring whereby the diaphragm pulls a rubber o-ring off its seat which allows the fuel to flow between the o-ring and its seat.
Fuel contacts the o-ring, but fuel should not contact the diaphragm.

It's not a function of the diaphragm to keep fuel from leaking out between the surfaces that hold the diaphragm in position, as fuel shouldn't be in that area anyhow.

Perhaps the o-ring or its seat is damaged??

Perhaps the diaphragm cover is being over-tightened during re-assembly?? It only need be snug enough to prevent vacuum leak.

Am unfamiliar with a "pressure relief hole" or why it would be needed.

Good Fortune!

If its like this then the same as I have. All he parts there and correct?

Howdy Bill. Is the replacement diaphragm a dealer item or K&L? Or made in china?

Just some info... After digging around the diagrams at Kawasaki.com, I believe a late mode police petcock can be used, 2005 or so... just in case you're interested in getting a new oem unit.

Fuel has been swelling up rubber components for years and years. Many times, even back in the 80's when CV carbs were the norm, the diaphragms would be so swollen very badly when the carbs were disassembled.

Allowed to dry up overnight, they seemed to shrink back down again.

It's possible the petcock sealing o-ring is swollen enough to let fuel get by between the o-ring and the piston.

But that's not the whole story either. The fuel needle seast itself should shut down the flow 100% but often times they don't. That's the reason for the vacuum petcock to begin with. It's a band-aid in reality.

A lot of times what happens with the vacuum petcock is a piece of debris finds it's way past the petcock screen and get's between the o-ring and port hole.

If you use some fine abrasive paste [smoker's tooth past with a little baking soda addes] and as QTIP, you can lap the port hole in the petcock to smooth it up.

It also works well on brass fuel needle seats. 550's with TK carbs were problematic when they were still relatively new bikes. We used to lap the fuel needle seats on those carbs to get them to quit overflowing. It generally worked pretty well.....

The whole point being that if you are going to try to cure a problematic fuel overflow problem......don't lay all the blame on the petcock. Look downstream at the last check valve point as well.

I'm not on a yearly program, but I have bought my share of these. I usually get the K&L ones, but figured things just aren't made like they used to be.

I belong to another forum an it seems to be the consensus there that the replacment diaphragms many times are DOA and that an aftermarket non vaccum operated petcock is the way to go.

+1 on the fuel swelling! When I took my bowls off my CV34's (750) the o-ring was way to big to even try and put them back together. Allowed to dry overnight and fit like a glove. So, if I ever take my carbs apart, it is a 2 day job minimum .

If you measure center to center on the mounting bolts you should be able to find a non-vacuum replacement.