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?

Lazerbubbles, December 2012

Valve timing is suspect. Fuel going in and blowing out is bad. Fuel will get into the oil so if it does start the engine will sieze. You put it together wrong. tear it down and try again

Bob, January 2013