I solved a pesky Zenith Model B carb leak last month that had defied stopping. I did all the usual things, such as changing the float level, installing a "modern" needle and seat, new gaskets, checking for cracks, etc. Still, there would always be a drop of gasoline each morning on the bottom of the main jet plug. I even tried a couple different drain plugs, brass and steel. No change. Drips continued, smelling up the garage.
I looked up on-line recommended fuel-proof sealants and found that Permatex Permashield Gasket Dressing, #85420, had good reviews. I bought a tube of it @ about $15.00 and applied it to the threads of the new drain plug I selected. I also bought a softer gasket at the hardware store that promised to compress better than the hard fiber gasket that typically comes with rebuild kits. This stuff stopped the leak overnight! No gasoline drips from the drain plug any more. I still shut the gas valve off after stopping the engine, but if I forget and go back into the garage the next morning, there is no gassy smell. The needle and float are doing their job and the Permatex sealant is doing its job. I think that perhaps the threads in the lower half of the carb body were worn oversized, which allowed gasoline to eventually by-pass the plug gasket. Anyway, this sealant really works at stopping gasoline drips. It might be a good idea to also smear some of this stuff on the on/off valve when installing it into the gas tank.
Try using this stuff on your drain plug and see if that solves the leaking problem.
Marshall
