Sounds like the carb is leaking down past the bowels. You need to rebuild or replace it. Sorry to be the bearer of bad news but I have been dealing that problem since 1985 . If you decide to rebuild it make sure to epoxy the lower bowls on the underside of lowest part of carb . Use a A@B mix epoxy like JB weld. also make sure to change the float ! Its a cheap fix if you do it yourself. A shop will charge ya about 3 hrs labor. (if they are nice) new carb is the way to go... 350.00 $ rebuild it yourself...50 bucks. . Also make sure to add a new filter to the deal pal!