[kz1000st]

I'm not discounting your problem but two petcocks rotting seems very odd to me. I have the same petcock as the scoot came with, six years later, and it works fine. Are you running an additive in your fuel? Also, given the picture of your manual petcock, where is it located on the bike. Mine is on the bottom of the tank. It doesn't surprise me that Chinese plastic would give grief, but twice? They usually either work or not, restricting flow is usually not part of their issues.