Vacuum petcock question

I recently replaced the diaphragm on my petcock. It stopped the spurting leak I had coming out of the side of the body but now I have another kind of problem. I put it back on the tank today and noticed that fuel was coming out of the petcock in any position. I followed fitz's rebuild guide and I am sure I did whatever needed right. Right now, the vacuum line doesnt have any clamps on it, could this be the problem? Could I have done something wrong in replacing the diaphragm? What can I do to fix it?

Right now, there is no gas leaking into the airbox, the crankcase, or the ground. So I guess thats a good sign about my carbs lol.

 

The Aftermarket Kits are a waste of time and money.
They are NOT from the Manufacturer and cannot be made exactly to the design patents held by the Manufacturer.
Close is NO Cigar.

You have to go to Yamaha for a Kit that fits.
The Manufacturer ONLY sells Kits to Yamaha for sale as a Yamaha Part.
Non-OEM Kits leaks.
If you don't believe me, ... ask you!

If the Kit you get doesn't have a Yamaha Parts Logo and Bar Code; it's a knock-off.

The BEST course of action to bring a leaking Petcock problem to an end is:
Buy a NEW Petcock.

The Original Petcock worked for a quarter of a Century.
A Part that good is worth the money!
And YOU can do without the aggravation!!!

 

Then why have so many, many people (including BigFitz) successfully rebuilt their petcocks with aftermarket kits?

P.S. the manufacturer makes original petcocks (and parts) for many different companies besides Yamaha...........

Raven, if fuel is coming out of the fuel outlet port in any position, without any vacuum being applied to the diaphram, then either the selector lever distribution "valve" is not seated fully, or is worn or torn, or the back face of the selector lever isn't fully flat....or, the wave "spraing" washer is not seated properly on the recessed area of the face of the selector lever, and this not putting enough (or an even amount of) pressure onto the selector lever to hold if "flat" and tight against the distribution valve.

On the backside of the petcock, the o-ring seat face is not perfectly smooth (typically, this will result in a somewhat slow, drip-drip-drip chinese water-torture type of leak), or, the o-ring is damaged, or, the diaphram spring is weak (or, the diaphram is not properly seated on the spacer plate and/or the vacuum diaphram cover plate).

 

If it's not shutting off, like Len said, most likely the o-ring isn't sitting on the seat properly.

How bad was the seat, did it polish up perfectly smooth?

You might be a candidate for a new spring, the replacement is slightly longer than the oem.

The other possibility is the selector valve but unless you forgot the wave washer it's almost impossible for that to leak-- you did replace the round black neoprene thing with the four holes in it, right?

You might want to pull it back apart and have a look.

I've successfully rebuilt a few of these but there are some things that you can't fix; then it's replacement time. Of course, my preferred replacement is a different pre-owned one that I CAN rebuild...

 

...or.. if th fuel is coming out the 'front' of th pet chook..is th O ring fitted to th edge of th selector lever and th wave washer placed between th selector and th cover (where it says on / off) with th 2 screws....

 

Well, um ...
Excuse me.
Let's have Mr. Peabody set the Way-back Machine to:
August 21, 2006
4 whole years ago.
http://xjbikes.com/Forums/viewtopic/t=1 ... fixed.html

BigFitz isn't the only guy to get one of those knock-off to do the trick.

I did, too.
I had to find a way to make it work.
Just like Fitz did.
Mess around with it. Alter the product. Fabricate. Reinvent.

Now, I'm saying that having to do all that is ridiculous.
It's a total waste of time and money.

The Kit Parts ought to come right out of the package and not need to be altered, fitted or rearranged or substituted in any way shape or form.

If it ain't going to work right out of the bag; it ain't worth buying!
Simple and sweet.
The consequences for using an ill-fitting Kit vastly outweigh spending the extra money for a Brand New Petcock.

You can search the web and find a New one for under 50-Bucks.

(FUEL COCK ASSY 1 33M-24500-00-00 1 $67.58 $46.94)

 

So have thousands of other people, no modifications necessary to the kit, although the proper preparation of the petcock body itself can be the deciding factor.

Not a MODIFICATION to the petcock body, but a RESTORATION to get it back to somewhat original functional condition.

Perhaps the kit that you used, Rick, was defective, or a brand that was not correct for your petcock (or, the petcock itself was not the correct one for the kit used)? I know that many of the used tanks that we see and receive have non-original petcocks on them; typically, the owner has no idea whether the petcock is "correct" for their tank/bke, or not.

In any case, as experience clearly shows, the original petcocks can be successfully rebuilt with the proper attention to procedures and a little bit of time and effort to do the job correctly, and with no modifications to the rebuild parts needed......

 

This becomes a logic puzzle.

Some leaking Petcocks can successfully be rebuilt.
Agreed.
Not all Petcock Rebuild Kits will leak.
Some Rebuilt Petcocks leak.
Why?

Because all Petcock Rebuild Kits are not the same.
How do you identify the Kit that will NOT leak?

The Member said he went through all the steps of Fitz's marvelous Photo-essay!
He must have got his hands on one of those Kits that don't work.

 

Wow, that's some type of logic.........!

Raven, please feel free to contact us and we'll be glad to assist you in resolving the problem, rather than having your situation remain un-resolved due to back-and-forth bickering and ranting of someone who has a (dull) axe to grind.

 

It's time for me to chime in again, since we're discussing my work.

Point 1: I never recommended nor do I advocate any modification or alteration of the kit. It should not be necessary; at the most a replacement diaphragm spring might be in order-- as long as:

Point 2: The petcock BODY you are trying to rebuild has to be in "rebuildable" shape. That includes the valve seat as well as the valve body where the selector lever o-ring rides.

If the seat is pitted or corroded so that it won't polish out to a nice smooth, even, new surface (I included a pic of a non-salvageable seat in my how-to) then it's a lost cause.

Likewise, if there is a serious groove worn in the body where the selector lever o-ring sits that won't polish out, then once again you need to find a better candidate for rebuilding.

Also, all "mating" surfaces need to be carefully inspected for pitting and corrosion, and "dressed flat" as I illustrated, or they can leak.

The bottom line:

NOT ALL PETCOCKS CAN BE REBUILT. SOME ARE JUST TOO FAR "GONE" TO BE SAVED.

I am aware of the "bell out the washer" trick to get the diaphragm in the large body petcock to seal; but I have never done it and have never felt the need. A replacement spring is usually all it takes. That being said, I have rebuilt a lot more of the "small body" units, and with great success.

REPLACEMENT is not always the best option; the "moderne" replacements do not exactly match all the various original incarnations, and in some cases either don't fit or barely fit; or stick out like a sore thumb especially on a restored bike.

Between my three XJs I have one new-style replacement and two rebuilt units that work fine.

REBUILDING successfully IS possible; but with a few caveats as discussed.

 

'Mr Petcock' here, don't repair petcocks & this from a guy who repairs anything, a repaired petcock has the potential to ruin your life / garage floor / shoes & your sump's integrity, speak to Mr Chacal & have him send you a nice new one, at a very reasonable price & live happily ever after.

 

Take the HOURLY LABOR Rate charged by a reputable Shop.
(In the Greater Boston Area its $90.00 per Hour)
Times 2 Hours for REBUILDING Petcock.* Maybe more.*
$180.00
Add price of Kit.
$ 25.00
___________
$205.00 Time and Materials.
<><><><><><><><><><>

New Petcock: $90.00
Shipping: 10.00
_________________
Uh hunnet dolless!

Divided by: 25 Years = $25.00 per year.
Divided by 12 Months = $2.10 per month.
Divided by 4 weeks. = $0.50 a week.
Divided by 7 days = $0.07 a day.

If a Petcock only costs $0.07 a day.
It's not rebuildable.
It's disposable.

 

Okay, now that's much better logic!

Although, the dollar values are a bit off, because $ 100.00 divided by 25 years life expectancy = $ 4.00 per year (rather than $25/year), etc.....so the per-day cost comes out to $ .0110 per day.

 

Well the petcock has always worked fine before I took it off. The only problem it had was it was leaking from the back side where the diaphragm is. So I only replaced the diaphragm since I just wanted to fix where it was leaking from the petcock body itself. It no longer leaks from the body BUT it lets gas flow through it now. Im not sure exactly which o-ring you guys are talking about unless it is the one that is on the diaphragm? I made sure to get the mating surfaces smooth and flat following fitz's wetsanding technique for the petock-diaphragm, but I didnt rip through the petcock to replace a small leak. So it was working before, now it isnt. So I wonder if I might have done something wrong.

If nothing else, if it cant be figured out I will go with the on off switch to go after the petcock. But I would really like to make this functionally right, since I am pretty much going through the entire bike.

 

Raven, on the "backside" of the petcock body is where all the vacuum diaphram parts live:

- the vacuum diaphram(s) themselves
- which are attached to the plunger "disc"
- which has an o-ring on the very end of the plunger disc shaft
- and that o-ring seats into a 30-degreee bevelled "seat" cast into the petcock body.
- there is also a small spring that provide pressure against the plunger disc that forces the o-ring against the bevelled seat and seals off the fuel flow thru the petcock when no vacuum is acting on the diaphram (i.e. when the engine is off, or if the vac hose is disconnected or broken, etc.).


If that o-ring is not seating fully into the bevelled seat in the petcock body, or, if the seat is scored, pitted, burred, etc., or if the spring is weak......in other words, any flaw at all on the seat that doesn't allow the o-ring to fully seal against the seat......the fuel will flow thru the petcock even when the engine is "off"....the petcock will behave AS IF there is always vacuum present on the diaphram, which is designed to pull the o-ring off of that seat (when the o-ring is off of the seat, that's how fuel flows thru the petcock, from the gas tank inlet to the fuel outlet in the petcock body).


Unless the spring is missing or mis-placed inside the unit, the plunger tip o-ring, if not fully seated, typically tends to allow a small drip-drip-drip type of action.........slow, but constant.

Possible causes of a drip-drip-drip type of leak:
- o-ring is damaged
- bevelled seat has a flaw (use a magifying glass if you are over 25 years of age!
- diaphram is just a bit not aligned properly in the spacer plate...the alignment holes in the outer edge of the diaphram popped off the small alignment "pegs" that are cast into the spacer plate, and thus the diaphram is not held taut and in alignment.
- spring is weak or is misaligned, not setting properly in the recess in the vac cover plate or not setting properly on the diaphram plunger stem.


If, however, the fuel flow is "full on, unrestricted" when the engine is off, then that suggests that the o-ring is not seating in the bevelled seat AT ALL:

Possible causes:
- o-ring is missing, fractured, damaged
- diaphram spring is incorrect, broken or missing
- diaphram is horribly not aligned properly in the spacer plate...the alignment holes in the outer edge of the diaphram popped off the small alignment "pegs" that are cast into the spacer plate, and thus the diaphram is not held taut and in alignment.



If you did not take the front end of the petcock part (the selector lever side), then the problem is probably not occurrinag from any of the components in there.

 

My sincerest apologies. I did omit that part from the pictorial because my camera did it for us but truth be told I'm WAY older than that and I do use a magnifying glass, all the time. (I also have one of those lamps with a magnifying glass built into the front of it.)

It is quite possible that the original seat has become worn thru time and the original o-ring fit the wear; where the new one might not.

I might also add that I never immediately trust a rebuilt petcock; I install it on a spare tank, and "cycle" it a few dozen times (gentle use of my Mity-Vac) then let it sit for a few days over a paper towel that will reveal a drip even if dried.

That being said I also have to admit that I have a brand new "moderne" one on my '83 550, and it is much more obvious than the original and JUST clears the carb hats. It's the only one that fits, the other styles won't fit at all, including the one Yamaha claims is for the 550 Seca.

Sore thumb.

 

So for the petcock, must I check to make sure I have the diaphragm in properly again? Where can I find a replacement spring?

 

What type of leak are you experiencing (slow drip or pouring out)?

I'm afraid that may be the next step in the process.

Send me an e-mail or a PM and I'll be glad to send you a replacement spring, we need to get your problem solved before damage or hazard consumes you!

 

Its more of a pouring out than a drip. Im wondering if I didnt do something with the diaphragm right since I dont remember doing this before, I couldnt shake the gas tank to get gas to come out really from the petcock. But if I am to open it again, I suppose replacing the spring would be a good idea. When I do open it again, what should I check for? Was I supposed to rub vasoline into the diaphragm? I think thats what I read from Fitz's guide. Could too much cause it to not function right?

Thanks guys.

 

Don't use vasolene or even KY.

 

Arg! I totally misunderstood Fitz's tutorial. I read through it too quickly and put silicone grease (sorry not vasoline) on the diaphragm.

"Now let's start by giving all the rubber parts a sparing wipe with silicone grease, and let's get the diaphragm ready to go on"

Could this be the problem? Is it possible to just clean everything off the diaphragm and reassemble?

 

It was OK to use silicone grease on the diaphragm, you just need to be sure it's rubbed in and used sparingly.

When you seat the diaphragm, make sure the spring is in the right place and that ALL the pegs on both sides of the plastic plate are through ALL the holes in both diaphragm leaves. Get your backing plate in place, and start the screws. Wiggle the rear plate around a little bit to be SURE the pegs on the spacer all engage the diaphragm and that the diaphragm sits down flat against both the body and the back plate before you tighten the screws.

If you have the petcock completely apart, you can see what's going on to some extent through the fuel supply holes.

Be sure to clean up and carefully examine the seat for any pitting or wear. Otherwise the new o-ring won't make a good seal.

 

Simple solution that worked for me... as long as your petcock is not leaking from the side seal, go to advanced auto, purchase a lawn mower fuel shutoff switch (2.99). Intercept petcock and fuel filter, install, put a few belt clamps on it, leave your fuel switch on on, and manually shut off the fuel from the lawn mower switch. Works great!

 

Thats what I plan on doing if it doesnt work. Im hoping I can make the petcock work just fine though. Ill probably take it apart again today and see what happens. Wish me luck!

 

http://www.maxim-x.com/petcock.html

 

I've been trying to follow this discussion but I could use some advice on where to find a new diaphragm.

I have a 83 xj750 and well the diaphragm is bad. My man tells me its hard to find oem diaphragm and from this discussion it sounds like oem is the best.

I found this site, http://www.z1enterprises.com/detail.aspx?ID=308 , but they are out of stock currently of sept. 29th.

Does anyone know where i can find one? and reasonably priced?

 

Mlowther, we carry a complete line of petcock rebuild parts---and even brand new petcocks and fuel valves---just drop us a PM or an e-mail and we can get you the info you need. In stock, too!