I owned a 62 buick with a 4GC. It had a dashpot on the throttle which when letting off the gas would allow the throttle to slowly return to idle. I know that when this was broken the car would stall when letting off the gas and braking. During high speed turns, the car would stall and I think due to fuel sloshing around in the fuel bowl uncovering the jets. These carbs also can have float adjustment troubles. Sometimes if they flood and you cant understand why, the problem is the back of the float hitting the inside wall of the float chamber when it rises. Take off the float and hold the swivel pin area of the float all the way against the back wall of the float chamber, the rear of each side float should just barely touch the back inside wall of the float chamber. Also check float alignment with the gasket off and air horn upside down with no needle valves. Float should be well centered and exhibit only slight side to side rocking. Each float ought to touch the air horn at the same time so the flotation pressure of both floats will be equal The best level is 1 3/8 on the primary and 1 5/8 on the secondary. The carb also has an internal fuel connection between the primary and secondary sides to equalize the fuel levels in each bowl. I currently have 2 4GC's in a boat and when the boat rocks side to side the engines do slightly cut out. I suppose again due to fuel sloshing around in the bowls. I personally dont think these are very well designed carbs. 4MV is better, if it would fit which is unlikely.
