I have an issue with my 1980 CB750C leaking gas from the carb overflow drains as soon as the fuel petcock is turned open. It just started doing this last summer right before I parked it for the winter. Also when the fuel petcock is shut off it won't run itself out of gas like one would expect, it just idles away happily. Anyone have any ideas as to what would be causing this symptom? I'm stumped.