which gasket to block heat crossovers?

[Musicman]

The carb is new as in I installed it last fall.  I was always under the impression that "boiling" meant the fuel was evaporating out of the carb and that's why it took so much pumping.  Am I better off flooring it while cranking?  Just barely depressing the gas, or pumping while cranking?

Every car is a little different of course... Personally, in a case such as this, I will start with the pedal barely depressed, then slowly press the pedal while cranking until the engine fires up. It usually lights off about halfway to the floor, which is about 2 or 3 seconds of cranking on the starter. I prefer not to hold the pedal to the floor if I can avoid it, as this causes the engine to fire off at a higher rpm. It is sometimes unavoidable however, as I said, all cars are a little different.

[71 SE3834V]

 

It helps to understand what is happening when you push down the pedal. Each time you push the pedal it will pump more fuel in via the accelerator pump. If you fuel is boiling/percolating there is a pressure build up from the heat and you will usually see fuel dripping out of the venturi if you look down the air horn. Not fun to do on a hot engine!
If you pump the pedal you will make it worse. If you hold the pedal down part to all the way, you will allow more air into the engine which will clear out the flood. Most carbs are setup to unload the choke (open it) a 1/4" or so I believe, if you open the throttle all the way (floor it) in case you flood a cold engine when the choke is closed.