Sounds like the carburetor needs some serious attention, also you need a fuel shut-off valve in the gas line. If you can't or don't know, how to fix the problem, better seek professional help, or the engine might go "BANG"!! At which point, your evident neglect of the machine will cost some bucks to fix it.

to amplify rusty's reply, yer carb is allowing raw fuel right on thru into the engine's crankcase. DO NOT RUN engine until contaminated oil has been drained, new filter installed and fresh crankcase oil added. The contaminated oil will not properly like your engine causing premature catastrophic failure.
M/W, find/correct cause of carb leak and - per Rusty's suggestion - spend a cuppla bucks to put in an inline manual fuel valve - and use use to shut fuel off to the engine every time you shut it down/put it up. Cheap insurance.You can get them at any shop that service lawn tractor engines.