Have you checked to make sure the float is closing? Years ago, I forgot to run the carb dry before the winter on my 1953 JD 40. Apparently, there must have been some water in the carb and it froze during the winter. The float was made of metal and was crushed a little by the ice. That caused a crack to form between the two soldered halves of the float and the float filled with gas so it could not close. I discovered this when I noticed I was using a lot of gas and then saw it running onto the ground. When tearing down the carb, I found the cracked float, drained and dried it out, and re-soldered it. It has been fine ever since.
