Hi Sean,
I would be seriously looking at the carby. Needle must be stuck and flooding (Badly). How many times did you pull it over with the spark plug removed? (Fuel tap OFF too) if it's flooded that badly you'll need to pull it over continuously for a good minute or two to to clear the fuel.
When it did run did it fire from the exhaust? (Loud bang often confused with back fire) If this occurred it's because of fuel igniting in the hot exhaust. This would have been caused by too much fuel being pulled through.
If it was hunting (revvs up and down) in this case it's because it was getting too much fuel and not enough air.
All points to flooded in my opinion. Easy fix assuming it hasn't been forced and nothing has been compressed and bent ...
Good luck. Pete
