1) You have a total of 8 rubber boots 2 sets of 4. They have to placed onto the manifold and carb with an orrentation. If not they will leak.
You need to have a stop in between the clamps, this prevents over tightening of the clamps, which will cause a leak.
2) There is a small o-ring when you remove each carb top, do you have them?
3) There is an orrentation with each rubber carb slide diaphram are they correct?
4) Make sure your carbs are fully seated to the boots, you may think they are fully on, but they may not be seated fully. Compare each one to ensure they are all seated properly.
5) How are you checking your rubber slide diagphram? Are you holding them over a light and stretching them to check for pin holes? (Use common sense not to tear them)
6) Remove the manifolds from the block, is there any silicone on any of these surfaces? Shouldnt be!