Wally,
The first time I rebuilt a carb and didn't use the gaskets, the wipers didn't run very well do to a vacuum leak, and the local antique parts store suggested using the above and below the insulator to help the seal better since the plastic doesn't conform very well to any irregularities at the carb or manifold. My old insulator was made of wood, which was softer and sealed pretty well, but split in two when I took it off. Don't know if the wood was original, but it worked well. I soaked the new gaskets in gas for an hour to soften them up, then installed them and they seal great. Good luck
