After Danny (sLick415) reported that taking his petcock apart and putting it back together solved his problem, I decided to do the same with mine. I took a look and saw something seemingly quite different from Andrew's problem though the defect is likely the same.
Like Andrew's defective petcock, the ring inside is not round. The major difference is that, instead of an incomplete ring, mine had what seemed like excess material blocking the opening and stains where the gas had been leaking out. When looked at from above, you can see some of the material forming a film slightly covering one side of the opening such that the ring is not round. The edge of the film is jagged.
In case this excess material was blocking the center pin from seating fully and causing my petcock to leak, I decided to see if I could correct it by removing the excess film. Sure enough, it fell right off by simply touching it with a pick. It turns out that wasn't the problem at all though.
The whole thing was pretty rough and dirty so I decided to clean up the rest of the petcock as best I could before putting it back together. I wanted to make sure that everything else would seal as well as possible, so I rinsed the rubber and other small parts and cleaned the exterior with 97% isopropyl alcohol and cotton swabs. When I was done, I decided to see if the interior stains inside would wipe right off, so I VERY delicately touched it with another wet cotton swab only to make another discovery: The "stains" were actually old gas trapped inside hollowed-out portions of the ring material which collapsed as soon as it was touched, now replicating the problem Andrew had exactly.
As it turns out, what looked like stains around the opening were gaps in the material with an extremely thin film over it. Touching it caused it to flake off completely. When reviewing my earlier pictures I can see what looks like a spiral of the material going even deeper into the petcock. It seems clear to me that this is the displaced material from a bubble in the mold when the ring material was still liquid.
I do wonder just how many petcocks are like this because many people never know theirs even leaks and most who do just replace it (very few people investigate). It may be something Kawasaki and Taiyo Giken have already identified and addressed with later production years using an extra QA check or with steps to prevent bubble formation or whatever causes this, but I do see plenty of 2011/2012 "leaky petcock" threads. If the EX250L/EX300A/B use a similar petcock and the problem has not been fixed, we need enough new owners to check and discover it within warranty for Kawasaki to take notice.
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Alex @
choneofakind