Need help rebuilding petcock

84tele · Sep 18, 2014

I'm cleaning and rebuilding my '78 petcock and the inlet tube was badly corroded. After a good cleaning, it has a visible hole (more like a split) in it that was underneath all the corrosion.

Are these inlet tubes brass or copper? It seems like copper.

Can I just solder-repair it or should I try to find a replacement tube? I would rather replace it if I can find a tube that fits.

Thanks in advance for the help.

XS400NJ · Sep 18, 2014

If mine broke - I would replace petcock with a simple one that is not vacuum operated. One less point of failure and no need to deal with that annoying vacuum line every time I need to take fuel tank off. (And I am losing the instinct to close petcock after ride).

xschris · Sep 18, 2014

It should be brass. Is it the tube going to the carb? Take some pics of what you have.

84tele · Sep 18, 2014

Here's a picture. If you look closely at the tube you'll see what looks like a split.

So, if I go with a new aftermarket petcock, which do you recommend?

I have a '78 XS400E that I'm restoring. Everything is original on it, but 26 years of neglect has taken it's toll.

Even the carb floats have developed holes. :doh:

XS400NJ · Sep 18, 2014

You may be able to find a piece of fuel line that will fit snugly on the tube over the crack, that may work.

BBS360 · Sep 18, 2014

I quite like knowing, when I turn my rebuilt vacuum petcock, that I've seen and cleaned every square millimeter of it.
It works great.
Vacuum petcocks have a bad rap but there's no downside.

xschris · Sep 19, 2014

That tube is for pulling at a higher point in the tank or your "on" position. There should be another small hole next to it that is your "res" position witch pull from the bottom of the tank. Most of the petcocks for the 400's I have seen don't have the metal pipes in them but a plastic filter and tube insert that allows that to happen. My guess is at some point the plastic one failed and someone put that pipe in so not to pull crud off the bottom of the tank. I would fix the hole if you want to help from getting bottom crap but make sure you have a good in-line filter between the carbs and petcock.

84tele · Sep 19, 2014

Actually on mine, the plastic filter slid over the brass tube. But, the filter was too far gone to save.

84tele · Sep 19, 2014

So, I bought a petcock rebuild kit and I'm not sure how to do this. I've seen the great thread with lots of pics (http://www.xs400.com/forum/showthread.php?t=8033), but it really doesn't help me understand how to fit this new kit to my original petcock. I'm assuming the old accordion diaphragm is discarded and replaced with the 2-ply gasket. However, the middle hole on the plastic spacer is too small for the replacement diaphragm to fit through. Do I need to disassemble the 2-ply diaphragm or something? I really need help. I've never done this before.

The accordion diaphragm was attached to the stem of the top diaphragm that fits through the hole. As you can see from the photos, the shaft of the new diaphragm is too big to fit through that hole in the plastic spacer.

Norman1950 · Sep 19, 2014

Over on xs650.com here is a link that might help...

http://www.xs650.com/forum/showthread.php?t=20662

84tele · Sep 19, 2014

Thanks for pointing me to that thread. I had come across that before at some point. I do notice the plastic spacer on his has a hole probably about the size of a dime, whereas mine is about the diameter of a pencil. I'm wondering if I will need to enlarge the hole on mine to make the new diaphragm fit. Has anyone else had this problem?

xschris · Sep 20, 2014

My guess is that your petcock must have come off another model bike. I have never seen a xs400 or xs650 with a plate or diaphragm like that. It may also explain the metal tube in it.

84tele · Sep 20, 2014

Hmm. In that case I have no idea what petcock this is or what bike it came off of. That's gonna make it difficult to rebuild.

84tele · Sep 20, 2014

Here are the parts to the petcock that was on this bike.

xschris · Sep 21, 2014

This is what the back should look like. You could just put a non-vacuum one in it. This is what I did with my 80. http://www.mikesxs.net/product/20-0019.html

84tele · Sep 21, 2014

xschris said:
This is what the back should look like. You could just put a non-vacuum one in it. This is what I did with my 80. http://www.mikesxs.net/product/20-0019.html

Are the mounting holes on this one the same as for the xs400-E?

xschris · Sep 21, 2014

They should be. Yours is the tear drop right.

84tele · Sep 22, 2014

Are you referring to the shape of the tank? See pic. Hopefully the distance between the mounting holes are the same.

xschris · Sep 22, 2014

Same tank I have. The only thing is the fuel outlet is on the same with the mikes petcock and you need to do a little finagling to clear the pullout choke. I have a xs360 carbs noe but it will work with the 400 ones also.

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