Everyone may be on to something with the cam timing.We had an engine that came in that had the cam lined dot to dot and wouldn't run.Came to find the dot to dot was the wrong refrence one dot was at the came gear and the other was at the crank keyway slot when it should have been at the crank gear tooth.The dot crank keyway was the designation for the retard tooth setting.Rest the crank gear tooth slot dot to the cam gear dot and it ran fine.There were 3 setting at the crank gear a retangle for retard a triangle for advance and a dot for straight up.The installer mistook the retangle for dot.Never use the mark at the keyway as a setting for the cam use it to position the related mark at the tooth area.This is worth investigating.