The Stovebolt Site Forums The Shop Area Engine Shop Carb problems

If the diaphragm is cracked or split even a little bit, raw gas will be sucked into the chamber below the diaphragm (it is constantly under vacuum) and from there right into your manifold. Another problem (which in your case I am less willing to suspect) is a warped bonnet...the one that holds the diaphragm assembly down. If this is overtightened, the corners will pull down warping the surface of the bonnet. I've seen these with between .006" to .010" of warpage and that will let fuel be sucked past and into the diaphragm chamber...where it goes into the manifold. I showed how to make a simple tool to fix this with a flat piece of wood and some sandpaper a few years ago. Jon has some diaphragms which are supposed to be resistant to ethanol laced fuel. They're orange. I've had good luck with one.