That is likely fuel running from the throttle shaft. It shouldn't do that on the scondary but it can do that on the primary.
Did you look inside the carb while the engine is running or with the fuel pump running? What causes fuel on the throttle shaft is when you shut the engine off a few dribbles come from the booster and land on the throttle blades which are closed because the engine is turned off - we are talking in a millisecond type time frame here.
The fuel dosn't just run into the engine as much as it runs down the throttle shaft and exits the carb at one side or another.
The problem i see is taht the fuel is on the secondary and since it is sitting in the garage and if the engine has been run it has just been run on the primaries so there should be no fuel any where near the secondaries. That is why you are going to have to look down in it when either the motor is running or the fuel pump is turned on. It sounds to me like the rear float is too high and needs adjusting down, we just have to prove that that is in fact the case.
I hate those carbs, i have a pair of them right now on a tunnel ram that i am trying to get sorted out - just hateful things the 4160.