simplicity 12 rth lawn mower b & s 12 hp motor

last summer my lawn mower was running rough and finally died and wouldn't restart, so i parked it and used my back up lawn mower. but since i need my simplicity for my snow blower attachment i need to get my mower running. heres what has been done and still having issues.
- i rebuilt carb changed oil and added ethenal free gas (gas came out threw muffler and still leaked gas that was in tank.)
-Now i have purchased a new carb installed, changed oil and it ran great i had parked it in garage for 2 days and whatever gas was left in tank has leaked out again.no gas came threw the muffler. can anyone give me any other ideas what could possibly be wrong with my lawn mower. any help is greatly appreciated

 

Is there a shut off valve between the tank & the carb. If there is, did you shut it? Remove the spark plug. Does it smell of gas? Does the oil smell of gas?

 

Hello no there is no shut off valve on it never was.spark plug is wet with gas.oil was just changed this fri and yes it does smell like gas

 

If the oil smells like gas, the new carb is leaking. It needs to be repaired or replaced.

 

Simple test, remove the bowl on the carb. and lift up the float to see if it completely shuts off the fuel when lifted.
Looked inside the gas tank for trash laying on the bottom? Amazing how much junk can get in there.
Any larger gas powered piece of equipment I own has, or I'd added a fuel filer.
One tiny piece can stop the needle valve from sealing the fuel off completely.

 

After you solve the problem with the leaking carb, you have to change the oil again, squirt a few drops of oil, in the cylinder & spin the engine a few times to get back the compression. The cylinder is gas washed. Change the spark plug again, too.