that has only one hole,..on the bottom,.....right? there's not holes up and down the sides is there? just one single hole on the bottom to clean/clear?
Most of the time if you're not seeing fuel/oil outside of the engine seals, it's going to be either the cylinder base gasket, or much more likely the O-ring between the carb and the end of the intake pipe spigot.
You say you didn't buy a new Buna-N 16mm X 3mm diameter O-ring for your new bike setup?
Times a wastin', get to your AutoZone and pick up a few O-rings.