petcock diaphragm block hole, rebuild question...

[Bonz]

Thanks jetmech...

Don't see the individual petcock diaphragms, as the is all I am looking for. Interesting there are some listed as K&L on ebay but can't find them on the site link you sent.

The main thing I am looking for is the best diaphragms to use, as I'm sure some guys have discovered differences between the different places that sell them.

I am not happy with the ones from Parts n More, compared to stock they are nothing but paper thin. However, the rest of the kit seems to be fine, so with the partial refund they gave me I want to source better diaphragms.

Not worried about finding diaphragms, but want to get the best ones I can and hope that others have gone before and can give me a heads up.

[jetmechmarty]

Just diaphragm, but the brand is not specified.

http://www.georgefixs.com/servlet/th...0-XS850/Detail

I used the George Fix kits on mine. I really don't recall the brand or quality of the diaphragm.

[Bonz]

I've bought carb kits from Georgefix and been really happy.

As I recall they were K&L, but not certain as it's been a few years.

I'll shoot George an email, see if I can get any info.

[crazy steve]

You might want to make sure the mating surfaces on both the petcock body and diaphram cover are flat. While I haven't had an issue with one leaking like yours, I've also ran a fine file across both faces to make sure they're flat. Not all them were....

[ViperRon]

I just rebuilt my 1980 G petcocks and there are several things that I did that may help to ensure a good build. I got the kits I have from Mikes XS they are made by Sudco and what I recieved was as good as what was originally in the bike but not cheap. There are several things that can cause leaks in the petcocks that no kit will resolve. First rust or trash in the tank can work its way into the plunger area and break the Oring seal. Water in gas can cause issues with this also.

You have already been given the correct orientation of the parts by others here in this thread so i will not repeat it. The hole threw the internal manifold and assembly must be installed correctly. The left hand parts handle valve must go in the left and right in right.

The retun spring for the plunger tends to get weak and may need to be streached a little. Do not streach it far or the vacume may not be able to suck it open. The metal parts need to be really clean I used Tarnex and soaked them.

The metal parts of the petcock may be like mine and the metal may have fatigued to where when bolted together the screw holes meet before the rest of the surface. I used 2000 grit sand paper streached across a perfectly smooth flat piece of wood. I resurfaced all flat surfaces to the point the entire surface was level. You will see that the screw holes are at first the only part that touches. I would not do this to the internal block as it has nothing againt it to stress the metal. I used Qtips and polished the inside of the plunder hole to ensure the Oring had a good clean smooth surface to mate too. I also polished the inside of the handle ports so they would be smooth against the internal seal. When reasembling I used a light coating of oil on all gasket mating surfaces to allow them to slide into place and also make a good seal. When bolting down just snug all screws first and then go back around tightening. If you torque one scew tight and then do the others it can cause leaks.

The area where the petcock mounts to the tank tends to bend a little. To be able to get this smooth its easier to remove the filter. The filter becomes brittle and you have to use care removing it. I put mine in a boiling pot of water and used a knife blade to slowly work arround to break the seal then wiggle and rock the filter out. The filter mainly is tight arround the stud. To get it back in push in by hand and then put a thick flat blade screwdriver near stud and tap the screwdriver it will slide back in.

I then used the same block and sandpaper technique to resurface where the Oring seals to the tank.

This is way overkill in the approach but you are having problems so I thought I'd offer it as mine are working just fine now.

[Bonz]

Good input, ViperRon. That's exactly what I did with mine, which parallels a link about XJ petcock rebuild found in other threads on the forum.

I did have a bit of flash rust that developed in the tank after I used muriatic acid to clean it, so I wonder if any residual in there after I cleaned it out could be getting in the petcocks and keeping the o-ring on the diaphragm from sealing off the fuel flow.

I put a new spring in each petcock (from Ace Hardware) and they are a bit stronger than the old stock springs, so I think I have plenty of tension to close the diaphragm.

Polished the diaphragm o-ring seat, surfaces of the petcock and diaphragm cover, circle where the lever o-ring resides. I

The petcocks are apart on the bench right now, I'll give them a good "once more over" and see how it goes.

[motoman]

Good input, ViperRon. That's exactly what I did with mine, which parallels a link about XJ petcock rebuild found in other threads on the forum.

I did have a bit of flash rust that developed in the tank after I used muriatic acid to clean it, so I wonder if any residual in there after I cleaned it out could be getting in the petcocks and keeping the o-ring on the diaphragm from sealing off the fuel flow.

I put a new spring in each petcock (from Ace Hardware) and they are a bit stronger than the old stock springs, so I think I have plenty of tension to close the diaphragm.

Polished the diaphragm o-ring seat, surfaces of the petcock and diaphragm cover, circle where the lever o-ring resides. I

The petcocks are apart on the bench right now, I'll give them a good "once more over" and see how it goes.

Hi Howard, I would suggest using the old petcock springs. Pull on them just a bit to re-establish tension. The stronger springs you have gotten MAY keep vacuum from opening them in ON or RESERVE position. There IS a fine line there as to their opening OR closing correctly. Something to put in your memory when you reach that point and carbs don't get fuel cept in PRIME position.

[Bonz]

I have no problem with fuel flowing, putting it mildly. It will run out the vent hole in the petcock body and through the fuel line when in "prime", it will flow out the vent hole when in "on" and vacuum is applied, but will not make it through the fuel line, same for reserve.

[CaptonZap]

HH

Did you try the old diaphragms?

CZ

[motoman]

HH

Did you try the old diaphragms?

CZ

+1.............If the petcocks weren't shutting off properly, didn't necessarily mean the diaphrams are bad. I had mine apart some 7yrs. ago as they weren't totally shutting off with vacuum loss. Removed and took them apart, cleaned everything good, ever so lightly stretched the spring on both, put them back together with a light smear of dialectic lube on the gaskets so they could 'squeeze' out and seal, never an issue since and that's the only time they had ever been apart.

[Bonz]

Putting them back together tonight, double checking everything, polishing the main sealing surfaces again, checked that all surfaces are true, etc. Keep you all posted.

CZ, one of the old diaphragms has a small tear and for both new diaphragms to be installed with all new gaskets, etc and to have both petcocks with the same problem, it's a bit odd.

I can suck on each vacuum nub and the diaphragm unseats the seal nicely, and when I release suction, it seals up firmly. I can blow into either nub and it's like blowing into a coke bottle, no give and nothing leaks. When I suck on the nub, I can rest it agaisnt my lip and it will maintain the suction for minutes, so nothing leaking there either.

[CaptonZap]

HH

When you say nub, are you talking about the vacuum one, the one on the back side, or the one that goes to the fuel inlets on the carbs?
If you can maintain a vacuum on the back one, you have proved the outermost diaphragm does not leak.
Put the handle in the on, or reserve position, and try to blow into the fuel nub. If air comes out the filter tower, the seal on the seat is leaking. If air comes out the vent hole, the inner diaphragm is leaking.
Whew!

CZ

[Bonz]

CZ, you got me on the right track... Both petcocks would freely flow air out the fuel screen tower when I'd blow into them.

Even though one of the old diaphragms has tear, the other one doesn't... So, put an old diaphragm in and it worked. Closer inspection showed the o-ring diameter on the tip of the new diaphragm plungers were a bit on the small side. I had picked up an assortment of viton o-rings at Harbor Freight so found ones that were just a hair larger in OD when installed, and the petcocks are tight now.

I think I've got it finally.

Motoman- I cleaned everything up again before doing the above reassembly so thanks for your input as well.

[CaptonZap]

I think I've got it finally.

.

Gott sei danke!
I was almost to the point that I was ready to say "I haven't got a f##king clue", and abandon you to your own devices. LOL
CZ

[Bonz]

Yeah, you had pretty much tapped out your pool of knowledge, don't know what we'll do once you've done that.