Petcock: Rebuild, Replace, or Modify.

Background: My petcock is fine when the engine is off, but under vacuum there is a leak or spurt, depending upon engine speed, of gasoline coming from the rear facing part of that white spacer between the two thin diaphrams (can't figure out it's proper name.) Upon dissasembly and inspection, it was determined that there is a notch in the white spacer leading under the diaphram/gasket and allowing gas to flow to the outside of the petcock. Now, it doesn't look broken, it LOOKS like that notch is supposed to be there. Furthermore, I don't understand how that notch could have gotten there through any but purposeful means.

My questions: Is that notch supposed to be there? I noticed that rebuild kits don't include the spacer, does that mean that I need a whole new petcock? Can I plug the hole with some gasket sealant and see if that makes it work? (I'm all about "making it work" at this point.)

Thank you!!

 

The notch is suppose to be there, you need a new diaphram in it. When fuel leaks out of the hole it means the diaphram has a hole in it, time for a rebuild.

 

I went through that problem last fall, when running you could see a spritz of gas at the back, right hand side of the petcock. bought a rebuild kit and it all worked fine afterwards. took me a while to realize that you have to squeeze the diaphram through the piece with the notch though. hope that helps some.

 

Correct. The "notch" is on the vacuum side of the diaphragm and is intended, I believe as a pressure relief port.

mlew is correct in that if there is fuel leaking there you need a new diaphragm.

The petcock can be rebuilt, as long as the seat in the body (for the o-ring on the diaphragm) is in decent shape.

 

Can I get just the diaphrams? Everything else works fine. I took it apart and it seems easy enough to replace.

Actually, now that I think about it, I'm pretty sure my notch was on the fuel side of the thing. Are the diaphrams supposed to be thin and papery, like a plastic film? Maybe its fine, just put in backwards? I do realize that it is more likely that I am mistaken about its orientation, but I remember thinking it odd that there was a notch where fuel was otherwise supposed to travel.

 

http://www.maxim-x.com/petcock.html

Contact Chacal on this site for parts!

 

The diaphragms are like thin paper rubber, they shouldn't be "crispy." One of yours has a hole in it.

You get the whole diaphragm assembly; the key to the whole thing is the o-ring on the metal button and how well it seats in the body of the unit. The best thing is to polish the seat with a q-tip and metal polish, and then examine (under a magnifying glass if necessary) the seating area to be sure it's free of pits or grooves.

I'm rebuilding the petcock for my XJ650RH right now and working on a photo how-to article as I go.

Here's a seat that's beyond redemption, no way to polish out those craters. An unfortunate victim of sitting and corroding for a long time, it has to be replaced:




This one, on the other hand, has only a couple of minor wear marks in it that should polish right out. It hasn't been polished yet:



Perfectly salvageable. Stay tuned.

The groove in the plastic plate goes toward the body of the unit, pointed down and to the rear (viewed as mounted on the bike.)

If you look closely at the plastic plate, it has different contours on each side; the big flat round indentation goes toward the "washer" side of the diaphragm, the side with the little groove goes on the "button and o-ring" side.

This really IS rocket science. The guys that built the exploding space shuttle should have paid such attention to detail...