2000 Pontiac Grand Am Wont Start

A friend asked me to replace the head gasket on her car. The car has been setting 3 months so. The last time she drove it it was pouring smoke out of the exaust and over heating. The water pump was replaced shortly before because of overheating. So I replaced the head gaskets and all of the other seals on the top end. I cleaned everything in the process. When I crank the motor it turns then kicks back. I thought it was flooded so I pulled the plugs to air it out. It still does the same thing. It blows back through the intake. I hooked a OBD 2 scanner to it but it did not tell me anything. I think its the timeing but I dont know how to check that. Ive got Commpression, Spark and Fuel!