I think your running slightly rich. If you have leaks you'd be running leaning. But do check anyway. For the mixture screw, turn it just a 1/4 at a time and listen to the idle. I like to find where it first starts to drop, then turn it back out by an 1/8 or so. Remember, clockwise lean, counter clockwise rich for the stock cv carb. The bike must be warmed up to find the right tuning. Ride for 10 to 20 minutes. Adjust. Then go fr a test ride. If needed increase the idle with the idle screw.
Stall at 55: Did it cough and sputter or just died out? Stall at stop: Dont think this is electrical, but carb tuning, especially as you keep it going with a throttle blip. Another thought occurred to me, make sure your engine breather is free and clear. This is the tube that comes from the crank case (black, about 1/2 in diameter) and goes to the catch can by the battery. Engine needs to breath but i dont think it'll cause a stall at 55... ive been wrong before tho.
...Could the clogged breather cause the faltering coming to a stop?
I don't think so. Have you turned the carb yet when the bike is nice and warm? Did turning up the idle make a difference?
Compression test...warm, full throttle 158psi.