To set my floats I usually just turn the carb upside down and use some calipers or a good ruler and measure from the mating surface of the carb body to the highest point of the float. Not sure though if it is the same on the FCR carbs as the Keihin PJ Carbs.

Sorry if it is a dumb question but my bikes are all gravity fed carbs. Is there some sort of check valve or fuel regulator that maintains correct fuel pressure? Is the overflowing carb the first one that gets fed with fuel?