Engine requires 20 degrees of initial to idle well...

EDIT Just looked at the bottom video. Fuel is POURING out those boosters Try dropping the fuel pressure or dropping the fuel level

You should see EXACTLY NOTHING out of the boosters at idle. They often make a pop--pop - sound as fuel drops into the carb throats, or bacon frying if more so

The causes are:

Too much fuel pressure

Poor needles and seats, or junk in them

Fuel logged foam floats, or too high float level

And as you've already addressed, metering rods.

Also, a really poor situation with a big cam can exist if the carb cannot handle the idle needed for the cam, and the combination of not enough ignition advance, and then "making up" by cranking the idle SPEED screw way up. This causes the idle transfer slots to become uncovered, and the main system to start working.

People USED to drill holes in the primary butterflies, but nowadays you can usually take car of it with lots of initial timing, and sometimes adjusting the secondary stop so the rear barrells "crack" open a tiny bit.

Don't be afraid to crank the mixture screws OUT. That is what they are FOR