your carb's float boal gasket might be bad. thats the case on all my puchs, heh. it causes slow leaking of gas. its not so bad when it runs.. the engine probably gets so hot the gas evaporates before i can notice it.. but when it is off and sits it definitely leaks gas. you can just use it like this as long as you turn the petcock off when its not running.. or else you might try to ride one day and find that you ran out of gas.... that's what i do. cheaper than buying new gaskets
but yeah w/o knowing the location of the leak, who can say for sure... the float bowl gaskets are a common problem, though. look for gas pooling around the left top of the engine under the carb.