I am far from an expert in this area but here are a couple of observations.

My vent is a simple loop tucked in alongside of the carb and I have not seen/smelled fuel venting from the float chamber. I have read elsewhere that a 1/2" drill bit used as a gauge for setting float levels should result in proper float level with a slightly "loose" fit.

Needle height is important and float level gives you the gross fuel adjustment for the carbs. Just a thought here. remove the float valves from both carbs and see if they are different. I remember something about rear valve is different from the front and it is the length. I don't remember which is which, but it is to compensate for differing gross mixtures under g-loads in the float chamber. It has something to do with the way the floats hinge and the location of the bowls since they are on opposite sides of the carbs. I will have to check my notes when I get home.

Hope that helps. Work has been getting in the way of fun these days with travel.

Paul