Vacuum Petcock rebuild kit - FAIL

[jetmechmarty]

I've had a couple of failed attempts at rebuilding vacuum petcocks. I thought the o'ring was wrong. I tried that. No help. Currently, I'm running some manual taps.

@GLJ has solved the issue. https://www.xs650.com/threads/81-special.65260/page-4

I have an unused diaphragm from Dime City Cycles.
https://www.dimecitycycles.com/petc...?fits-motorcycle=Yamaha/XS650/all-models/1981

I measured the pin at 18.14 mm.

I measured four OE diaphragm pins. 18.75, 19.06, 19.06, and 19.02 mm.

I believe the diaphragm pins in the kit are at fault. Be aware before you buy.

EDIT: It says in the description that the pin is 18.5 mm long. That isn't long enough. I should have measured first, then read the description.

 

[GLJ]

@gggGary alluded to a work around/fix in my thread maybe he will expand on it.

Yup run into that short shaft thing before. There's a trick... I'd PM it, but it takes a practiced hand to work. If the screen assembly is a loose fit in the petcock, a bit of shim from a pop can will help keep it in place. Falling off happens, no screen, no reserve, when it does.

 

[XSTime]

Currently, I'm running some manual taps.

After years of praising Vacuum petcocks functions, here I am with the manuals Not leaking and looking quite promising

 

[jetmechmarty]

I believe the issue is K&L Supply 18-6633. That's the part every vendor sells. It's no good. No matter where you go, you get the same failure.

 

[GLJ]

I believe the issue is K&L Supply 18-6633. That's the part every vendor sells. It's no good. No matter where you go, you get the same failure.

Marty is the failure it won't shut off?

 

[jetmechmarty]

Marty is the failure it won't shut off?

That is correct. Fuel flows with no vacuum applied. My XS650SK has never had the petcock tampered with, and the bike has never been put up for extended time. The petcock is fine. It's the other bikes. I don't care for the manual petcock. I keep forgetting to turn it off.

 

[GLJ]

That is correct. Fuel flows with no vacuum applied. My XS650SK has never had the petcock tampered with, and the bike has never been put up for extended time. The petcock is fine. It's the other bikes. I don't care for the manual petcock. I keep forgetting to turn it off.

2 thoughts there. Since I'm used to early bikes shutting off the petcocks is second nature. Just something you do. If this auto works I'll have to get used to it.

 

[Jim]

Never measured the diaphragm pin length 'cause it never dawned on me it was too short, but my first try had a leak too. I put a fatter o-ring on the diaphragm pin. Leak free for about 5 yrs now.
https://www.xs650.com/threads/jims-1980-sg-miss-september.50545/post-591766

 

[jetmechmarty]

Never measured the diaphragm pin length 'cause it never dawned on me it was too short, but my first try had a leak too. I put a fatter o-ring on the diaphragm pin. Leak free for about 5 yrs now.
https://www.xs650.com/threads/jims-1980-sg-miss-september.50545/post-591766


View attachment 259931

View attachment 259932

I followed that and your advice. You sent me two of those o'rings. No joy. I went to the K&L website and made them aware of the problem. MikesXS gives a proper description. It just isn't correct for the Yamaha. My XS1100 vacuum shutoff has the same issue. Luckily, it has factory manual taps.

 

[gggGary]

@gggGary alluded to a work around/fix in my thread maybe he will expand on it.

Yup run into that short shaft thing before. There's a trick... I'd PM it, but it takes a practiced hand to work.

I take no responsibility for this working for you.
Went and looked, sure enough had an unopened K&L kit from the infamous cardboard box of parts that comes with every project bike.

The suspect

grab an 18mm-ish socket, stuff the diaphragms inside so the disk contacts the socket edge.

Gently tap the end of the shaft til the disk takes on a slight dish shape,

it's aluminum will bend easily. You only need a 1/2 mm or so. This effectively lengthens the shaft causing the o-ring to contact the seat a bit sooner. Check the disk is still at 90 to the shaft, the edge even.

It will be happy to warp, get all ugly if you overdo the tapping. Done.

IIRC correctly this fix has been in use on Madness' petcocks for ten-ish years.
Carry on!

 

[Jim]

You sent me two of those o'rings.

Yeah... I remember now.

 

[Mike G]

I had the same problem with mine. I read somewhere (defunct xs650 site?) about putting the diaphragm, pin down, on a socket and tapping lightly to cup the aluminum disc so the pin/o-ring can reach the seat. It worked for me and has been leak free for over three years and counting.

I’m too slow, Gary beat me to it and did a much better job to boot! His is probably the post I was thinking of. Never mind…

 

[jetmechmarty]

View attachment 259933
I take no responsibility for this working for you.
Went an looked sure enough had an unopened K&L kit that came in the infamous cardboard box of parts that comes with every project bike.
View attachment 259934
The suspect
View attachment 259935
grab an 18mm-ish socket, stuff the diaphragms inside so the disk contacts the socket edge.
View attachment 259936
Gently tap the end of the shaft til the disk takes on a slight dish shape,
View attachment 259937
it's aluminum will bend easily. You only need a 1/2 mm or so. This effectively lengthens the shaft causing the o-ring to contact the seat a bit sooner. Check the disk is still at 90 to the shaft, the edge even.
View attachment 259938
It will be happy to warp, get all ugly if you overdo the tapping. Done.

IIRC correctly this fix has been in use on Madness' petcocks for ten-ish years.
Carry on!

Thank you!

 

[gggGary]

I had the same problem with mine. I read somewhere (defunct xs650 site?) about putting the diaphragm, pin down, on a socket and tapping lightly to cup the aluminum disc so the pin/o-ring can reach the seat. It worked for me and has been leak free for over three years and counting.

I’m too slow, Gary beat me to it and did a much better job to boot! Never mind…

Think I posted this years ago, in the madness thread? prolly.
I fought those SOBs a good long while 'for I figgered out the shaft was short.

 

[gggGary]

While we're all here I DO NOT use aftermarket petcock 4 hole rubber valve either, Yamaha sells the correct part, the aftermarket are thinner.

 

[Mike G]

When I saw the pictures above Gary they looked awfully familiar, it was your post I was thinking of. You’da man!

 

[Melnic]

Macgyver would be proud. Nice mod gggGary.
I rebuilt my 2 petcocks and I tested them on the bench but have yet to wet test them in the tank.
Have 2 manual ones in there now, I'll have to remember this if mine leaks so I don't flip out right away.

 

[jetmechmarty]

Getting the manual petcock to work on the XS650SH was not as simple as bolting it up and connecting the fuel line. The quality of that petcock does not come close to OEM.

 

[mrtwowheel]

View attachment 259937

That's one funky unbalanced hammer there. No way could I wield that thing with precision, and I do have good hammer skills.

 

[gggGary]

That's one funky unbalanced hammer there. No way could I wield that thing with precision, and I do have good hammer skills.

Weighs about 8oz. Didn't you make one in HS shop class? I thought everyone did.