What I would do is-
Pull the spark plugs and ground the plug wire ends.
Remove air filter and open up throttle full (no choke)
Crank the engine over for 5-10 seconds and see if you blow a bunch of crud/oil out of the cylinders.
What do the plugs look like? If OK, reinstall them & wires, and try to start it.
EDIT: Forgot to ask-
HOW much did you overfill it?