Outside of having your timing correct, 1406's are a very simple carb. If you haven't a fuel pressure regulator on it, get one. What happens when its unregulated and there's too much fuel pressure, that pressure will bend the tangs on the float and it will eventually need a place to dump the extra fuel that's in the fuel bowl, it has only one place to go. Well actually 2 places. The 2nd place will require a fire extinguisher as it will seep out from where the airhorn mates with the carb body. Then onto your manifold.
If you pull the airhorn off, there are 2 cavities behind the secondaries. If those cavities are full of gas, that excessive fuel pressure is seeping between the airhorn and carb body.
Pull the airhorn off, check the float height and the float drop. Then put a fuel pressure regulator on it and see what your results are. Make sure the pressure regulator will adjust down to the 3.5-5psi range and stay away from the Mr Gasket dial type gauge. They're junk. Here's a link for you to look at. From there you can go to their tech center and checkout their videos.
https://edelbrock-instructions-v1.s3.amazonaws.com/edelbrock/carb-tuning-guide.pdf