jdl, im not familiar with vacuum asisted wipers, but if you are having that problem i would suspect a vacuum leak, either with the carb gasket or the intake manifold gaskets. exhaust gaskets would make the popping noise, but they would not affect your vacuum.
i do know that my hedder gaskets, that go between the hedder and the heads, they were burnt and there was a few leaks, and i would only get the small popping sounds at a cetain rpm, like around 1000-1500 rpm. anytyhing over that you really couldnt tell.
but if you do have a vacuum leak, say in the carb or intake manifold gasket, it will affect the idle quality.
i think, if while the truck is running, you can spray some carb cleaner around the bottom of the carb gasket, and around the intake manifold gasket, and it it starts to run BETTER, then you definetly have a vacuum leak in that area where you sprayed.
hope this helps.
leonard
