Petcock rebuild kit for XJ900/Maxim X is crap

XJ petcock rebuild kits are officially crap - at least as far as the XJ900 and Maxim X are concerned. They charge almost 40 bucks and send you the same rebuild kit that's meant for the XJ650 and XJ750. It works fine on those models since I've used it on my XJ650 Maxim with success.

But the XJ900 and Maxim X petcocks are very different. The rebuild kit's valve stem is too short and its head is the wrong shape, thus allowing gas to leak past even when the bike is turned off. Hap on the XJ owners email forum told me the only way to make it right is to put the valve stem and diaphram plate head down in a 12mm socket. Then use a 7mm socket on the back of the diaphram plate and push the plate down 2mm. This will make the valve stem taller, thus stopping gas from leaking past when the bike is off. It's a very touchy procedure that's easy to screw up by tearing the paper thin diaphram rubber or not bending the diaphram plate exact centered and the right height. I other words, YOU have to do the work of the a-holes that sold you what is really the wrong part. What a rip off.
Maybe it's just frustration talking but I'm spending the extra 10 bucks and going with chacal's manual petcock. I had one on my Kawi KLX and I'd remember to turn it on and off by putting a tiny red dot sticker on the ignition key housing. Worked like a charm and the petcock never ever leaked.
baz

 

HMMM...that's exactly what's happening with my Maxim-X petcock. I just replaced the diaphragm, the selector rubber, polished the face of the selector with the 2 channels in it, polished the plunger seat face, and it still lets the gas pour out regardless of where I put the selector. Seems like I might have wasted my time unless someone has a solution to my problem. It leaks out of the fuel line pipe like the selector was set to PRI. I measured the spring and even expanded it to 24mm without success. Does anyone have any other suggestions?

 

Baz: I got my pieces from Chacal, including the shim washer for the spring to help the new diaphragm seal better. Yes, I read the bit on Hap's site -- very informative, that. And yes, I sanded down the back of the selector lever as well.

 

Well, I gotta give credit where credit is due!! Minutes after posting this, I went down to the bike, took out the petcock diaphragm and tried the 2mm mod suggested by Baz. It actually worked perfectly! No more leak!! The only time it lets gas through is in PRI, just as advertised. I did one change to the procedure Baz suggested, and that was to use a 13mm long socket instead of the 12mm. In this way, the thin rubber diaphragm could be stuffed into the socket comfortably and with 2 taps of a hammer on the 7mm socket, the calibration was done. It really pays to search your topic before just posting a question. It was during my search that I found this topic in among over 700 topics with the word "petcock" in it. Awesome site folks...keep it up.

 

Well, I gotta give credit where credit is due!! Minutes after posting this, I went down to the bike, took out the petcock diaphragm and tried the 2mm mod suggested by Baz. It actually worked perfectly! No more leak!! The only time it lets gas through is in PRI, just as advertised. I did one change to the procedure Baz suggested, and that was to use a 13mm long socket instead of the 12mm. In this way, the thin rubber diaphragm could be stuffed into the socket comfortably and with 2 taps of a hammer on the 7mm socket, the calibration was done. It really pays to search your topic before just posting a question. It was during my search that I found this topic in among over 700 topics with the word "petcock" in it. Awesome site folks...keep it up.

 

Actually, the XJ700/900 petcock diaphram is a different part than the XJ550/650/750 diaphrams....completely different size of diaphram.

The problem with re-building these petcocks properly are many and well-documented, and the simple procedure that HAP on the www.maxim-x.com website suggests will work.....but if you read more carefully on that same site, you'll realize that the problem is not so much due to the replacement diaphram, but rather (or additionally) due to the petcock body itself.....not only is the plunger seat hole bored slightly off-center, but after years of use, the o-ring seat develops minor surface imperfections that allow fuel to leak past it.

That's why the factory used a HOLLOW o-ring on the business end of the plunger.....to compensate for poor production or machining tolerances in the first place. The replacement diaphram units do not have a hollow o-ring, and use the more conventional solid o-ring. A solid o-ring will obviously not deform much (or at all) to take up the variances in the plunger seat wear or mis-alignment like an original o-ring will.

In addition, the o-ring seating surface in the petcock body---and this applies to ALL of the XJ series petcocks, not just the XJ700 and 900 models---has to be inspected VERY, VERY CAREFULLY for scratches, gouges, etc. in that seating surface. Use a magnifying glass under strong light; you'll never see them with your own eyes if you're over 18 years of age. Those gouges and scratches must be somehow polished out or filled in for the petcock to not "leak" (even if it's just a slow drip-drip-drip type of leak) when the petcock is in it's ON or RES position. Fuel WILL find its way through and past those surface imperfections.

Luckily, the solution provided by gently "stretching" the plunger (via careful deformation of the disc) along with a shimming washer under the spring will allow enough additional pressure on the plunger, and thus on the solid o-ring, to allow it to seal properly.....assuming that the seat is in good shape and or re-furbished properly.

 

Chacal:

You're always the man with the answers! I agree with your suggestions on the plunger. Since I have a polishing setup, I used the white compound and a cone bob to reach in and polish the surface to a mirror finish. Coupled with the 2mm disc stretch, my kit has now stopped the leak. Many thanks to this topic thread and your dedication to the XJ bike!