T100 craftsman riding mower

The lawn mower is misfiring, key will turn and engine revs up but doesn’t turn on, sometimes it misfires. The lawn mower sat for two weeks, after which my mom put fuel in it that had been sitting outside that time without a lid on the canister… we had rain during that time also. I didn’t know she did this until after I did this: changed the spark plug (needed it anyway), put carburetor cleaner in the fuel holder, put a different kind in the air intake valve that said I could. After she told me I drained the fuel and put new in, still not working. Then I thought maybe not enough oxygen so I took the air filter off to start it, still didn’t work.
What do y’all think the problem is?
If bad fuel got to the carburetor do y’all think I need to take it off and clean it? Or maybe a starter?
Any help appreciated.