Tap the carb body a few times, w/something like a long socket extension, you may have some grit in the needle seat. If that doesn't do it, you will need to remove the carb rack and check the seat/needle, and check the float levels which you have 'em off.
Also you want to use a flashlight to check your gas tank for corrosion/rust. It has to be shiny-clean, unless someone used a tank liner treatment on it. Even then, if the lineer wasn't installed exactly as it's supposed to be, it can delaminate from the tank insides, and move to the carb valve seats for fuel flow, and cause that type of excess gas flow. If it was failed gas tank liner treatment I'd expect that > 1 carb was going to be affected. Also check your gas filter, when was the last time you changed it?
I cut-open the gas filter whem I'm changing 'em out to see what kind of crud it collected. Racers do that w/their oil filters too, see what's in there.
A cylinder leak-down test can help you to determine where the problem is. Sound at the intakes or exhaust means valves, sound at the oil filler means rings.