What type of carbs, when you tore the carbs down did you make sure all the ports (openings) were clean with carb cleaner and then use air compressor to spray? Sounds like you may have a opening not fully cleaned.
Or when you calibrated the carb cables. Did you do them off the engine? Stearing straight, carbs laid as flat and straight as possible?? then when you adjusted them give gas and relase a couple of times, then check to see if they are still the same?
Also how are the full filters or filter? and the hoses being that old. and the vaccum hose for the fuel pump??
hope some of the ideas help, not that you may not of thought of most of these.
Or when you calibrated the carb cables. Did you do them off the engine? Stearing straight, carbs laid as flat and straight as possible?? then when you adjusted them give gas and relase a couple of times, then check to see if they are still the same?
Also how are the full filters or filter? and the hoses being that old. and the vaccum hose for the fuel pump??
hope some of the ideas help, not that you may not of thought of most of these.