Repairing a Jawa Petcock
The petcock used by Jawa is unique in size and fitting, there are no after market replacements. This may be disheartening to learn at first but it's not all bad. In fact, you don't want another petcock; the factory one is probably one of the best ever made! It is a much heavier duty construction than most others and it's also extremely simple - making it a breeze to rebuild again and again. So get off eBay pick up your tools and follow these steps!
1- Disconnect and remove fuel tank, empty contents into an appropriate container.
2- Loosen collar nut.
3- Remove petcock, clamp gently in a bench vice leaving the lever accessible. (Now would be a good time to clean out that rusty tank. Got POR?)
4- Unscrew wire mesh (yeah, it's threaded!) then unscrew the lever retaining nut. The lever and disk valve will come out together.
5- You will see a rubber disk in the valve body with 5 holes, a drywall screw gently twisted in to the center hole will grab that seal nicely to pull it out.
6- Clean out the valve body and all its passages as well as the screen and any mating surfaces.
7- Examine the rubber disk seal. If the petcock was leaking or the seal is visibly damaged find a piece of gas resistant rubber and cut a new one, don't for get to drill the 5 holes. This is the only seal in the whole unit, so if it leaks this is why.
8- Reassemble and install petcock and tank.
9- Go ride your moped.