if the carb is overflowing it is prob the float needle is either worn or there is dirt stopping it from closing ,make sure its clear and check for signs of wear on the rubber tip of the needle when puttin it back make sure the float is closing properly
A good trick is to leave the bowl off the carb connect it to a fuel source[ hold it level as it would be in the bike] hold the float closed and turn on the fuel for a second just enough to let juice through, if it flows through with the float closed you have a needle problem if not let you float free and close it again with fuel running through and see if it stops again if it still stops well you have another problem
be careful no sparks etc
the only way in to a carb is through the float chamber so this has to be were to start looking from probs
hope this helps