[Jim Vander Wal]

This is not an uncommon problem.

Get the float levels set properly. High float levels in the back will probably aggravate the problem but you also don't want them too low and starve the engine for fuel when needed.

The fuel is forced through the system during braking. I had the same problem with a custom Holley 780 double pumper The builder did some magic and most of the problem went away.

Vent whistles will help and are recommended but not an absolute solution. I've tried most "solutions" and didn't find one on my own.

A new carb isn't a guaranteed solution. If a sales guys insists that the new carb will fix the problem, get it in writing with a return tag.

Jim