Petcock Rebuild

maximusrising

XS650 Enthusiast
XS650.com Supporter
Messages
51
Reaction score
46
Points
18
Location
Clinton, MA
Vacuum type, new soft parts. Drip, drip , drip this is the normal Run position, in Prime it flows freely, Res same drip
Since it's dripping from the fuel outflow port I think it's OK? But I do not know if I put the plastic block in correctly. Too stupid to pay attention when I took it apart. I think there are two ways it will fit, one is probably wrong.
 

Attachments

  • drip.jpg
    drip.jpg
    177.8 KB · Views: 123
Sounds like you are not getting a seal. You might pull it apart and check the spring ompression and have a look at the seat where the diaphram seals. You might have to stretch the spring and/or polish the seat.
 
Yamaha vacuum petcocks have always been trouble. Change them to old manual types.
The petcocks were replaced by Yamaha when they came out and the replacements also.
Rebuild kits are not worth the money as a small bit of dirt or erosion in the internal parts
will bring on a leak and fill your crankcases with gas if the bike is sitting on the main stand.
 
Dripping from the outlet is caused by the small o-ring on the diaphragm valve. Go to o-rings and more and order this seal.
Fwiw... I've rebuilt several of the vacuum petcocks and they work just fine.

z.jpg


x.jpg
 
I'm dealing with a slow drip on my right petcock. Is this seat too far gone? I'm going to order the o-rings Jim shows on post #4 but if the seat is toast I may look for another petcock. This is a XS750 petcock
IMG_2153.JPG
 
I'm dealing with a slow drip on my left petcock. Is this seat too far gone? I'm going to order the o-rings Jim shows on post #4 but if the seat is toast I may look for another petcock. This is a XS750 petcockView attachment 202611
Chuck a Q-tip into your drill motor with some rubbing compound. That might get it done. It will cost nothing to try. BTW, ethanol eats petcocks.
 
It's a little much for a q-tip. I put a stone in my dremel and smoothed it out somewhat then polished that out. Fingers crossed...
I ordered the o-rings from Oringsandmore.com but at first I had some trouble finding them. Here is what I got from their customer service dept:
Thank you for asking. The SKU for that one is a little odd. It is 3.52MMV. You can find them here: 3.52MMV
However, I purchased extra so if anyone needs a couple - hit me up.
 
FWIW,
the XS650's stock petcock don't have a true OFF position until it's pointed straight up.
You hafta cut the petcock's lever a tad shorter and file off the outer plate's little anti-turn nubbin to do this.
 
FWIW,
the XS650's stock petcock don't have a true OFF position until it's pointed straight up.
You hafta cut the petcock's lever a tad shorter and file off the outer plate's little anti-turn nubbin to do this.
My vacuum petcock has been working as advertised since I bought my bike 38 years ago. It only spent one winter in a cold damp barn up north and that was 1985/86.
 
My vacuum petcock has been working as advertised since I bought my bike 38 years ago. It only spent one winter in a cold damp barn up north and that was 1985/86.
Rebuilt mine comin' up on 3 yrs now... works as advertised.
Should add that was with genuine Yamaha parts. Don't think you'd get that lucky with Mikes rubber crap. Someone should check and see if Sumo Rubber across the pond sell the bits to rebuild one. The rubber bits I've bought from them is good quality.
 
Last edited:
Rebuilt mine comin' up on 3 yrs now... works as advertised.
Should add that was with genuine Yamaha parts. Don't think you'd get that lucky with Mikes rubber crap. Someone should check and see if Sumo Rubber across the pond sell the bits to rebuild one. The rubber bits I've bought from them is good quality.
The K&L kits I bought at George Fix’s Store have held up well for several years. I repaired my XS1100 fuel system with them.
 
I rebuilt the petcock on "Dad's bike" three seasons ago and it's still working well with no leaks. I polished the seat, used an o-ring from an HF kit on the pintle to see how well it would hold-up (so far so good), reused the diaphragm from the original petcock as it was in good shape and bought a new rubber disk from Yamaha to replace the brittle original. After rebuilding, I put a piece of vinyl tubing about two feet long filled with kerosene on the brass inlet tube to check for leaks figuring this was at least three times the pressure it would see in service and...drip drip drip. I tried stretching the spring but it didn't help. I read a tip about flaring the aluminum disk (using an appropriately sized socket placed on the pintle side) that the spring presses on to allow the o-ring to seat deeper and tested it again and there was no more leak. Apparently the aluminum disk was bottoming on the petcock body ever so slightly. No idea how you would check for that other than install it or use the kerosene in a tube like I did.
 
Back
Top