I have a 1981 Honda cx500c, I’ve rebuilt the carbs multiple times trying to chase this problem down. After rebuilding them the first time it was fine for a few months but then started. Fuel comes out of the bowl overflow tube. It comes out pretty fast. I cleaned the carbs and it has all new parts. There’s no cracks in the overflow tube. If I drain the carbs then it will be fine for a few days but comes back when it sits for atleast a day. I’ve been thinking it could be the pet cock as it is the vacuum operated one. I have a gravity petcock that I’m going to try. I don’t normally turn the fuel off but I drained the bowls yesterday, rode it around for a little bit and then parked it and turned the fuel off and will see if the problem comes back once I start it up again. Is there anything else that could cause this? I’ve gotten pretty good at taking the carbs off and can have them off in a few minutes. So it’s not a problem to me to have to take the carb off to check something. If yoy have any idea let me know. Also should point out that this bike sat for 15 years and that was the original reason for rebuilding the carb.