Petcock rebuild tip

While doing regular maintenance changing fuel filter. When I removed the fuel line from the petcock the fuel did not stop. The lever was set at "on”. Great!! I need a rebuild kit :twisted: .Went to a local Yamaha dealer and got a kit, Disassembled Cleaned petcock spotless cleanest part on the whole bike. Reassembled with all the new o-rings and seals. Added fuel to tank and it leaked :evil: worse then before. Took apart the vacuum diaphragm and figured that the large flange where the spring sits was not allowing the the o-ring to seat properly.

My fix to this problem was to put this flange in a 9/16 deep socket and tap the center down very slightly. Reassembled and all worked fine .
The kit was from "tourmax' part number 16-698

I hope this helps someone else.

 

Lostboy ... here's the Post I put-up when I had the same Brainstorm!
.......................
Everybody with that "Vacuum valve leak-by" ... Do this for THE FIX!

Pull the Vacuum valve off the petcock.
Using a 19mm socket as "The Table" and a Standard Small "C-clamp" as the Press ... PRESS the Center Spring Retaining Rod- ON THE ALUMINUM DISC SIDE -- IN ... .015 - .020mm Causing the aluminum disc to form a slightly concaved surface ... thereby moving the opposite side of that rod ... where the O-ring attaches ... to be moved .015 - .020mm further into the receiving taper of the valves O-ring seat. FIXED! DONE.

This is "The Fix" ... for "Petcock Leak-by"

Just another in the long list of inovasions brought to you by the World Leader in XJ-Series restoration techniques and shop tricks.

RickCoMatic ... They don't call me "RickCoMatic" for 'nuthin!

'Cuz wenn dat boa gots iz mo-jo woikin' ... yeh jess no sumpin' good gunna appin' ...

Kin ah gits ah Hey-men on DAT!

I fixed it ...
Copyright Aug 21 2006
Richard E Massey
Billerica, MA
The RickCoMatic Leak Fix

 

Thanks Rick great minds think alike. I hope I did not step on any toes.

 

There's another way to do this.......I sell a thin flat washer (HCP663) that fits into the recess on the vacuum diaphram cover plate (the outer cast aluminum plate)----this plate has a recessed "bore" in it where the diaphram plunger Spring seats. Adding a properly sized shim washer under the spring---in this recessed bore hole in the cover plate---increases the pressure on the spring, thus on the diaphram disc/plunger, and thus on the o-ring. Since you already have the cover plate off when rebuilding the petcock, this is also an easy solution fix. I've rebuilt petcocks both using and not using this shim, and whenever a brand-new diaphram unit doesn't cure an ON-RES position drip-drip-drip leak, the shim washer addition always does.

A related problem is that the machined bevel-cut seat in the petcock body---where the o-ring actually seats against and "seals" against---tends to get beat up after years, and if you look REALLY closely at it (like under a magnifying glass), you'll see some tiny flaws in the surface. These flaws translate into those leaks. I've made a special tool to use along with some very fine lapping compound to "refinish" and polish this machined seat, as it's very hard to reach by hand (if you have very small fingers, the tip of your pinky might work). If this machined seat also has any scratches in it, then you'll need a properly bevelled cutting tool to cut away a fraction of material---and then finish it up with the polishing routine described above.

Obviously, having a baby-butt smooth o-ring seating surface is a necessary requirement for positive, leak-proof sealing of the petcock fuel o-ring.

I would also recommend "surfacing" all the other mating surfaces on the petcock when rebuilding it, using maybe 400-600 grit wet-or-dry paper: the top (to tank) mounting surface, the cover plate(s) mounting surfaces, and the petcock body mounting surfaces (where the vacuum cover plate attaches), the flat side of the petcock selector lever, and the inside bore of the petcock selector lever bore. You'd be surprised as you start surfacing these areas how un-straight they actually are after all these years! And thus a potential source of problems....

I've never had a petcock (I've rebuilt close to 100 of them) that leaked after rebuilding, using the techniques described above. The "automatic" feature of the factory petcocks is a neat, handy feature to have. These petcock are simple, but like all other items on a 25+ year old machine, do need a little gentle TLC after all these years.......

 

Well.... I'm dragging this link to the desktop... for a winter project..
I had mine rebuilt, but I do get a slow leak. Plan to clean up the tank more once I put the bike up for the winter, adding this to the to do list as well.

 

No problem.
We're hear to solve problems.

It's a crying shame the Petcock Manufacturer won't sell rebuild kits to anyone other than Yamaha Dealers.

Although, I've about had it rebuilding Petcocks. If the New one will last as long as the Old one ... I'm just getting a new one and leaving the headaches out of the equasion.

 

You can also chunk the OE style vacuum "automatic" petcock and use an aftermarket "fuel valve" (= a true on-off style "manual petcock") which works very well, but you have to remember to turn them on and OFF every time or you'll either run out of gas soon after driving off (easy fix) or you'll flood your carbs every time you finish riding (big problem). And you have to enlarge the opening very slightly on the gas tank where the petcock bolts up to it. But it is another solution, as long as you can train yourself to ALWAYS turn it on and off (think of it as an extra ignition switch.......).

 

I'm sold on factory fuel valves, I've rebuilt 2 without issues. Chacal, if you have the tool and the know-how for refinishing the diaphragm seat, will you be offering this service? I'm sure you'll find a ready supply of work...

 

Hey Robert.....well, actually I do. Sorta. I have rebuilt original petcocks listed in my ad:

n) XJ's gas tank Used Original Petcocks, various XJ550, 650, and 750 models, work great! Includes new inside filter, o-rings replaced, cleaned, etc.
$ 59.00 + shipping. GUARANTEED NOT TO LEAK!

over at:

http://www.xjbikes.com/Forums/viewtopic ... rt=45.html

and I've actually rebuilt a few petcocks for some forum members, but I just don't get a lot of call for the service. I do sell quite a few of the petcock rebuild kits, and I hope that people do get them installed correctly and take all the extra steps (kinda doubt it, though) to insure that their petcock is in like-new condition.

Yes, I need to update it to list the 700, 900, and 1100 petcocks, too!

I guess I should list a "send in your petcock and have it rebuilt" service, but that adds another $5 or so for the shipping to me of a petcock, and with the costs of the parts and time involved to properly rebuild one, it would be about the same price as just buying one outright. As I run out of original petcocks I'll have to do that, or maybe add a "core charge" to the rebuild service.

I'm having the lower fuel outlet plate gasket made, and should have it available shortly, it's about the only part needed to rebuild an original petcock that isn't currently available (wasn't used on 650 Turbo, 700, or 900 models with the "big" petcock body).

The special cutting and polishing tools I had made for the o-ring seat is really what makes rebuilding the petcocks a no-brainer, fail-safe procedure. Before I made them, about half of them would leak even after the install of a new vacuum diaphram plunger/o-ring. Once I got out my 10x loupe and started looking carefully, I found out why: the original "o-ring" on the end of the vacuum plunger tip was either internally hollow or was originally "pyramid" shaped, to better contour to the bevel slope of the o-ring seat...thus not much seat pressure (provided by that diaphram spring) was required to seat the o-ring into the seat snugly, securely, and leak-proof.

The replacement diaphram plunger o-rings are true "o-rings", and are solid, and thus any flaw in the seat surface results in that slow drip-drip-drip after a rebuild.....a perfect sealing surface is required when using the harder, solid o-ring as is currently available in all of the rebuild kits. So you absolutely have to make sure that the seat is in tip-top shape, and that spring shim I use adds a little extra push to the plunger and helps seat the o-ring tightly.

BTW, the method that Rick outlined above accomplishes the same thing as what I'm saying, although I still recommend at least polishing the o-ring seat as a precaution (as well as surfacing all the mounting flanges on the petcock body and the selector lever face and bore). The risk is that if you push too hard on that disc, and distort more than the necessary amount, you might end up with a diaphram that won't ever be able to seal again. Of course, you can always still replace it, so it wouldn't be "game over" time for that petcock anyway!