troublesome Murray Select MS2550

[LilCerberus]

 Last month, the screws holding the jug on my Murray 2550 String Trimmer broke, & I wound up buying a new short block engine.
I had to pull the carb & coil, etc off the old one & put the on the new one.
The new one feels a hell of a lot stiffer when I pull the cord, takes forever to start, & won't run for too long.
The "stiffness" in the cord feels like the cylinder want to go one way, but not the other.
Any thoughts?