Honda x8r just wont start?

I have just changed my crankshaft. the scooter worked perfectly before i changed it, and everything is ok still. there is great compression in the cylinder, every gasket is ok, and there is a clean blue/purple spark, it just will not spark.... there is gasoline spewing through the exhaust too. sometimes if i turn the engine for a while, it kicks back, and there will pop a great flame from the exhaust, any help?