Edelbrock 1406 whistling
I have that intake AND that carb and I did not have to use an adapter or anything.....no leaks or whistles or anything. I even pulled my old eddy carb off when I bought a brand new 1406 and i took a good look at the gasket and it was sealed up great all around the intake side aswell as the carb side.
anyhow....my suggestion is....if your getting a leak around the intake to carb mating surface that is allowing it to suck air..... I am wondering if maybe you ran it hot one day and shut the engine off and allowed it to heat soak the aluminum of either the carb or the intake?
its a slim chance but there is a chance none the less.
I suggest removing to carb.....stuffing a couple rags in the opening of your intake. Then take a flat chunk of wood or whatever you can get your hands on .....wrap some sand paper around it (im not talking like 60 grit here.....just something to leave a guide line for you like some 320 or 400) ....just scuff the mounting surface of the intake.
if your intake is slightly warped and allowing air to be sucked in you will notice a spot or spots that do not have sanding marks on them.
if this is the case....I personally would sand a bit more until it was flattened out. .....or you could have it professionally done, or buy a new intake.
also check the carburetors mounting surface the same way.
and remember to remove the rags from the intake opening prior to reinstalling your carburetor lol