[F]I was an idiot and tipped my Murray Rider mower onto its side, flooding the carb and spark plug chamber with oil. After cleaning that all out and getting a new spark plug, I can't get the mower to start at all. Suggestions? Thanks!

Let it sit overnight. Pull the plugs and see if there is oil in the cylinders. If so then slowly get the position to its highest point in the cylinder and use a clean soft rag and a small screw driver handle in the rag and wipe out excess oil. No turn the starter to blow the cylinder. Install plug.

Check the gas float in the carb fuel bowl. They can get stuck when you flip the mower. Sometimes the needle seat valve that lets the gas in the carb bowl gets hung up also. That would flood the bowl and carb and even dump excess gas in the crank case oil .

It's the carb here that's not happy.

Check crankcase for gas in it just to make sure it doesn't have gas in it. Smell the dip stick and look for small bubbles on the stick.

Change oil if you suspect gas in the crankcase.