A lot of times when an engine is over primed, it will run backwards. You should be able to spin or snap the spinner backwards and start the engine. It bounces on compression going backwards, fires and starts forward. I start nearly every engine this way.

On an engine that big, never pull the prop through compression like you do a .40. If it backfires it has enough power to break fingers. A buddy of mine broke his on a Moki 1.8 like this.

Put the prop up against compression like you were going to start normally, but twirl the spinner backwards. It should start in a couple of tries.