wtf petcock...wtf

[Mickey85]

81 xs400, working on the petcock. Pulled it last fall and rebuilt it, and it promptly leaked all of the gas tank into the crankcase. I Pulled the tank and dumped in a gallon of gas, and it ran out immediately, whether I plugged the vacuum poet or not, or whether or not it was on "on" or "reserve". Rebuilt it again, same problem...

So, a, is there anything I'm missing, and b, is there a manual on/off petcock that will fit a stock 81 tank without an adapter?

 

[rshutchinson]

I believe its usually the spring gets weak and the o-ring on the diaphragm doesn't seal.

 

[Mickey85]

That'd be great if you could check that for me! Thanks!

 

[rshutchinson]

No problem. In the mean time you can try two things.

One option is to take the petcock apart and pull the spring to decompress it or add a nut behind the spring. That should keep it from leaking.

Other is to go and get a lawnmower on-off valve. They're plastic and you can just splice it in to your line going to the carb. Then leave your tank petcock on and just use the plastic one.

Look like this:

 

[hurricanepaul]

Right on, just installed one on my bike last sunday when having float issues, wish I had more room to fit gas filter.

 

[ScottLuke]

I bought this one off Ebay. Price is a little steep, but well worth it. Hutchinson, are you sure that will fit the XS400, I tried ordering one before the one below, and it was too small. http://www.ebay.com/itm/230844156979?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

 

[Wolfe_11B]

I bought this one off Ebay. Price is a little steep, but well worth it. Hutchinson, are you sure that will fit the XS400, I tried ordering one before the one below, and it was too small. http://www.ebay.com/itm/230844156979?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Hate to tell you now, but MikesXS sells that petcock for $48.

 

[kshansen]

No problem. In the mean time you can try two things.

One option is to take the petcock apart and pull the spring to decompress it or add a nut behind the spring. That should keep it from leaking.

Other is to go and get a lawnmower on-off valve. They're plastic and you can just splice it in to your line going to the carb. Then leave your tank petcock on and just use the plastic one.

Look like this:

You know I was just starting to have problem with my XS650 float(s) or vacuum petcock or probably both, anyhow that is just what I was planning on installing today! A better idea than the needle nose vise-grip pliers I have been using!

It's my rat bike/sidecar outfit I ride to work and as I'm going to be retired the end of next month I just need to get a few more weeks out of it. Then I may make it a restoration project and fix things right.

 

[rshutchinson]

Hutchinson, are you sure that will fit the XS400, I tried ordering one before the one below, and it was too small.

Just measured and you are absolutely right. It's 34 mm which I need and the XS tanks are 46mm. I removed the link to avoid confusion.

 

[ScottLuke]

Sweet baby Jesus, I am returning mine and buying Mikes. $73 vs 48! Lol

 

[arfstrom]

http://www.maxim-x.com/petcock.html
http://xjbikes.com/forums/index.php?threads/rebuilding-the-yamaha-vacuum-fuel-valve-w-pics.25058/


Okay, before you dismiss this link, this is the same petcock that our bikes use. This is a very good web sight. Like previously mentioned, the spring could be weak, but I like to support the theory that the problem is highlighted on this link. The current seals/orings do not make it to the sealing surface. so my recommendation is to put a smaller oring behind the bigger o-ring, which will push it out, and (forward) so that when the diaphram is not in vacuum mode, it will press up against the sealing surface.

This is the item I bought to implement that solution. It is nice to pull the fuel line off, and not see it leak, as soon as the tube is off.

viton 0-rings "4 MM X 1 MM BN70" from
http://amzn.com/B000RBZ8C2
I bought them for carb job. it was a 5 ring pack, I only needed 2. I have to admit, that the shipping for one package, Blows.... .99 cents USD, and $10.00 shipping. Check local resources like Fastenal, or Menards, Lowes, ... (etc)