So I have this cb750K2 with a leaky petcock, I don't ride it much and am trading it to my brother for an engine I don't want, therefore it needs fixed. I rebuilt it recently but bought another kit, obviously made in china. I removed the valve, sanded the tank bottom, cleaned the petcock top, replaced the o ring, put it back in. Now it has aluminum tank screw to petcock body washers. They leaked through, I greased them and overtightened them with my JIS screwdriver. They finally appear to hold but the sediment bowl still leaked. Several different tries and o rings later, I left it turned off and blew into the gas line. Fuel sprayed sideways out of the sediment bowl. L0L!
There is a tiny pinhole in the bowl. I swapped it with another one and, it's finally fixed.