ORIGINAL: Rudeboy
Jett and Nelson racing engines are so tight when new you can hardly prime them by hand... they will most likely get stuck, unless you have a very strong, fast "flick" in your wrist.
Half of the time you even have to run up your electric starter before you hit the engine with it, to prevent a sticking piston.
This description is exactly what has been happening with the K&B 3.5 that I've been breaking in. I just bought a backup that's also never been run and although I won't actually try to turn it over until I'm ready to run it, it appears it will be the same.