If an engine is really loaded up from over priming, it will kick back hard when the engine is cool, usually won't fire at all if the engine is hot, a situation which can fool you into priming it even more. Sometimes the engine will even oscillate.
The cure, pull off the fuel line from the carb and keep trying to start it. Every time it runs for a small burst, that's so much less fuel pooled up in the crankcase. Eventually it will clean out and run strong for a couple of seconds before running dry.
Now hook up the fuel line and choke the engine just until the fuel reaches the carb and no more and it should run when you flip the prop.

Always start the engine with the throttle closed to idle, it's actually easier to start that way.